feat: rework just file and add code coverage generation

[DeveloperPaul123]

Fixes #55

[Copilot]

Pull Request Overview

This PR reworks code in the engine by updating arithmetic operations for score calculations and adjusts test behavior, and it adds workflows for coverage reporting and improved build configurations.

• Marking a long-running test as ignored.
• Replacing direct arithmetic with saturating operations in score calculations.
• Adding GitHub Actions workflows for code coverage generation and a configurable build matrix.

Reviewed Changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 1 comment.

File	Description
engine/src/search.rs	Added #[ignore] to a test to bypass potential timeouts.
engine/src/score.rs	Updated arithmetic operations to use saturating math.
.github/workflows/coverage.yml	Added a new workflow for code coverage generation.
.github/workflows/build_and_test.yml	Updated build workflow to support multiple Rust versions and build types.

Files not reviewed (1)

• Justfile: Language not supported

Comments suppressed due to low confidence (1)

engine/src/search.rs:651

• [nitpick] The #[ignore] attribute disables this test, which may reduce test coverage; consider adding a comment explaining why the test is being ignored and under what conditions it should be re-enabled.

    #[ignore]

[codecov-commenter]

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[DeveloperPaul123]

Regression test:

Elo   | 0.35 +- 3.14 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=16MB
LLR   | 2.98 (-2.94, 2.94) [-5.00, 0.00]
Games | N: 24122 W: 7391 L: 7367 D: 9364
Penta | [893, 2622, 4996, 2668, 882]
https://pyronomy.pythonanywhere.com/test/1778/

[DeveloperPaul123]

Possibly a very small elo gain with the score bug fix

Elo   | 0.81 +- 2.08 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=16MB
LLR   | -2.96 (-2.94, 2.94) [0.00, 5.00]
Games | N: 52878 W: 16157 L: 16034 D: 20687
Penta | [1769, 5808, 11260, 5735, 1867]
https://pyronomy.pythonanywhere.com/test/1793/