Add examples sections to docstrings of characteristic curves in sympy.physics._biomechanics

[brocksam]

References to other Issues or PRs

Forms part of the CZI biomechanics work program described in #24240. Follows directly on from #25441, #25509, #25516, #25519, and #25530.

Brief description of what is fixed or changed

This PR adds examples sections to the class-level docstrings of the characteristics curves in sympy.physics._biomechanics.curve where they're missing.

I have not added any documentation beyond docstrings, nor have I added the docstrings to the online documentation yet. For the reasoning above this would likely need significant rewriting after any API changes. Documentation will be contributed in a future PR when the whole biomechanics module is moved to sympy/physics/biomechanics.

Other comments

I have specifically left the release notes entry empty. These will be added in the PR that moves the whole biomechanics module to sympy/physics/biomechanics.

Release Notes

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#### References to other Issues or PRs
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Forms part of the CZI biomechanics work program described in https://github.com/sympy/sympy/issues/24240. Follows directly on from #25441, #25509, #25516, #25519, and #25530.

#### Brief description of what is fixed or changed

This PR adds examples sections to the class-level docstrings of the characteristics curves in `sympy.physics._biomechanics.curve` where they're missing.

I have not added any documentation beyond docstrings, nor have I added the docstrings to the online documentation yet. For the reasoning above this would likely need significant rewriting after any API changes. Documentation will be contributed in a future PR when the whole biomechanics module is moved to `sympy/physics/biomechanics`.

#### Other comments

I have specifically left the release notes entry empty. These will be added in the PR that moves the whole biomechanics module to `sympy/physics/biomechanics`.

#### Release Notes

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* solvers
  * Added a new solver for logarithmic equations.

* functions
  * Fixed a bug with log of integers. Formerly, `log(-x)` incorrectly gave `-log(x)`.

* physics.units
  * Corrected a semantical error in the conversion between volt and statvolt which
    reported the volt as being larger than the statvolt.

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[github-actions]

Benchmark results from GitHub Actions

Lower numbers are good, higher numbers are bad. A ratio less than 1
means a speed up and greater than 1 means a slowdown. Green lines
beginning with + are slowdowns (the PR is slower then master or
master is slower than the previous release). Red lines beginning
with - are speedups.

Significantly changed benchmark results (PR vs master)

Significantly changed benchmark results (master vs previous release)

| Change   | Before [8059df73] <sympy-1.12^0>   | After [191a72d6]    |   Ratio | Benchmark (Parameter)                                                |
|----------|------------------------------------|---------------------|---------|----------------------------------------------------------------------|
| -        | 94.3±5ms                           | 59.3±0.4ms          |    0.63 | integrate.TimeIntegrationRisch02.time_doit_risch(10)                 |
| +        | 22.7±0.9μs                         | 40.9±1μs            |    1.8  | integrate.TimeIntegrationRisch03.time_doit(1)                        |
| -        | 7.20±0.03ms                        | 3.92±0.09ms         |    0.54 | logic.LogicSuite.time_load_file                                      |
| -        | 2.19±0.1ms                         | 670±20μs            |    0.31 | polys.TimePREM_LinearDenseQuadraticGCD.time_op(3, 'sparse')          |
| -        | 10.7±0.4ms                         | 1.99±0.01ms         |    0.19 | polys.TimePREM_LinearDenseQuadraticGCD.time_op(5, 'sparse')          |
| -        | 378±8μs                            | 82.5±0.2μs          |    0.22 | polys.TimePREM_QuadraticNonMonicGCD.time_op(1, 'sparse')             |
| -        | 5.10±0.3ms                         | 368±1μs             |    0.07 | polys.TimePREM_QuadraticNonMonicGCD.time_op(3, 'sparse')             |
| -        | 10.8±0.04ms                        | 1.11±0ms            |    0.1  | polys.TimePREM_QuadraticNonMonicGCD.time_op(5, 'sparse')             |
| -        | 6.51±0.2ms                         | 4.03±0.01ms         |    0.62 | polys.TimeSUBRESULTANTS_LinearDenseQuadraticGCD.time_op(2, 'sparse') |
| -        | 27.7±0.08ms                        | 12.3±0.02ms         |    0.44 | polys.TimeSUBRESULTANTS_LinearDenseQuadraticGCD.time_op(3, 'sparse') |
| -        | 7.24±0.1ms                         | 1.21±0.04ms         |    0.17 | polys.TimeSUBRESULTANTS_QuadraticNonMonicGCD.time_op(1, 'sparse')    |
| -        | 16.9±0.5ms                         | 9.79±0.4ms          |    0.58 | polys.TimeSUBRESULTANTS_QuadraticNonMonicGCD.time_op(2, 'sparse')    |
| -        | 213±0.3ms                          | 71.8±0.2ms          |    0.34 | polys.TimeSUBRESULTANTS_QuadraticNonMonicGCD.time_op(3, 'sparse')    |
| -        | 6.64±0.2ms                         | 547±2μs             |    0.08 | polys.TimeSUBRESULTANTS_SparseGCDHighDegree.time_op(3, 'sparse')     |
| -        | 29.0±1ms                           | 873±3μs             |    0.03 | polys.TimeSUBRESULTANTS_SparseGCDHighDegree.time_op(5, 'sparse')     |
| -        | 626±10μs                           | 201±0.8μs           |    0.32 | polys.TimeSUBRESULTANTS_SparseNonMonicQuadratic.time_op(1, 'sparse') |
| -        | 6.73±0.2ms                         | 204±1μs             |    0.03 | polys.TimeSUBRESULTANTS_SparseNonMonicQuadratic.time_op(3, 'sparse') |
| -        | 17.8±0.7ms                         | 209±2μs             |    0.01 | polys.TimeSUBRESULTANTS_SparseNonMonicQuadratic.time_op(5, 'sparse') |
| -        | 168±10μs                           | 97.4±3μs            |    0.58 | solve.TimeMatrixOperations.time_rref(3, 0)                           |
| -        | 328±10μs                           | 117±7μs             |    0.36 | solve.TimeMatrixOperations.time_rref(4, 0)                           |
| -        | 33.3±1ms                           | 13.8±0.04ms         |    0.42 | solve.TimeSolveLinSys189x49.time_solve_lin_sys                       |

Full benchmark results can be found as artifacts in GitHub Actions
(click on checks at the top of the PR).

[moorepants]

This looks fine to me.