Add copilot-instructions.md

[RyanCavanaugh]

🤖

[Copilot]

Pull Request Overview

Adds a new contributor guideline file for Copilot workflows, detailing linting, formatting, test paths, and commit structuring.

• Introduces .github/copilot-instructions.md with step-by-step bug-fix and test-baseline procedures
• Specifies commands (hereby lint, hereby format) and expected test duration
• Clarifies where to add test cases and how to organize commits for baselines

Comments suppressed due to low confidence (2)

.github/copilot-instructions.md:10

• [nitpick] This sentence is missing a connector. Consider: "Add the test and its baselines in one commit" to improve clarity.

 * Make a testcase that demonstrates the behavior. Run it (by itself) and review the baselines it generates to ensure it demonstrates the bug. Add the test its baselines in one commit

.github/copilot-instructions.md:3

• The path test/cases/compiler seems inconsistent with tests/cases/fourslash. Consider using tests/cases/compiler to match the existing folder structure.

 * Only add testcases in `test/cases/compiler` or `tests/cases/fourslash`. Do not write direct unit tests.