[decimal] Implement sin() and cos() for BigDecimal

[forfudan]

This pull request introduces significant enhancements to the BigDecimal module, focusing on trigonometric functionality, precision handling, and modular arithmetic. It also updates documentation and test cases to support these changes. The most important changes include the addition of sin and cos functions, improvements to rounding precision methods, and modular arithmetic support.

Trigonometric Functionality Enhancements:

• Added sin and cos functions to struct BigDecimal, with range reduction and Taylor series implementations for accurate calculations. These functions handle edge cases for π-related values and ensure high precision. (src/decimojo/bigdecimal/bigdecimal.mojo src/decimojo/bigdecimal/bigdecimal.mojoR765-R774, src/decimojo/bigdecimal/trigonometric.mojo F4fb1110L30R321)
• Updated arctan function to use round_to_precision for consistent precision handling and added intermediate result handling for better readability. (src/decimojo/bigdecimal/trigonometric.mojo F4fb1110L56R355)

Precision Handling Improvements:

• Replaced round with round_to_precision across multiple functions, adding options to remove extra digits due to rounding and prevent trailing zeros. (src/decimojo/bigdecimal/constants.mojo F7b2c265L166R322, src/decimojo/bigdecimal/rounding.mojo src/decimojo/bigdecimal/rounding.mojoL102-R104)
• Added detailed notes in the round_to_precision method to clarify the behavior of precision-related parameters. (src/decimojo/bigdecimal/bigdecimal.mojo src/decimojo/bigdecimal/bigdecimal.mojoR848-R854)

Modular Arithmetic Support:

• Introduced the __mod__ method in struct BigDecimal to support modulo operations, leveraging truncate_modulo. (src/decimojo/bigdecimal/bigdecimal.mojo src/decimojo/bigdecimal/bigdecimal.mojoR526-R534)

Documentation Updates:

• Expanded documentation in docs/internal_notes.md to include examples and precision comparisons for sin functionality, highlighting discrepancies between Decimojo, WolframAlpha, and mpmath. (docs/internal_notes.md docs/internal_notes.mdL5-R16)

Test Case Enhancements:

• Refactored trigonometric tests to include sin and arctan functions, enabling modular test execution through a reusable run_test function. (tests/bigdecimal/test_bigdecimal_trigonometric.mojo tests/bigdecimal/test_bigdecimal_trigonometric.mojoL14-R45)