fix(polys): fix printing elements of EX[x]

[oscarbenjamin]

References to other Issues or PRs

Brief description of what is fixed or changed

On master printing elements of a ring with EX domain fails:

In [1]: str(EX[x].from_sympy(x))
---------------------------------------------------------------------------
SympifyError

This is due to PolyElement.str attempting to compare an element of the ground domain with an element of the ring. In the case of EX comparing with a PolyElement raises. Possibly that should be fixed but at least here we make sure that we are comparing elements of the same domain in str.

Release Notes

• polys
  • A bug that prevented printing elements of polynomial rings over the EX domain was fixed.

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• polys
  • A bug that prevented printing elements of polynomial rings over the EX domain was fixed. (#24248 by @oscarbenjamin)

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

On master printing elements of a ring with `EX` domain fails:
```python
In [1]: str(EX[x].from_sympy(x))
---------------------------------------------------------------------------
SympifyError
```
This is due to `PolyElement.str` attempting to compare an element of the ground domain with an element of the ring. In the case of `EX` comparing with a `PolyElement` raises. Possibly that should be fixed but at least here we make sure that we are comparing elements of the same domain in `str`.

#### Release Notes

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statements. The basic format is a bulleted list with the name of the subpackage
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* solvers
  * Added a new solver for logarithmic equations.

* functions
  * Fixed a bug with log of integers.

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<!-- BEGIN RELEASE NOTES -->
* polys
    * A bug that prevented printing elements of polynomial rings over the `EX` domain was fixed.
<!-- END RELEASE NOTES -->

Update

The release notes on the wiki have been updated.

[oscarbenjamin]

The underlying error is this:

In [6]: EX(1) == EX[x].one
---------------------------------------------------------------------------
SympifyError

Generally == should return False rather than raising an exception. The way to do this is just to have __eq__ return NotImplemented if the other operand does not have the expected type.

[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)

       before           after         ratio
     [41d90958]       [ae895046]
     <sympy-1.11.1^0>                 
-     1.28±0.03ms         804±20μs     0.63  solve.TimeSparseSystem.time_linear_eq_to_matrix(10)
-     3.54±0.08ms      1.55±0.01ms     0.44  solve.TimeSparseSystem.time_linear_eq_to_matrix(20)
-      6.74±0.2ms      2.24±0.04ms     0.33  solve.TimeSparseSystem.time_linear_eq_to_matrix(30)

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