feat: add custom instructions for copilot

Author: peter-jerry-ye

.github/copilot-instructions.md

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+# AI Coding Agent Guidelines for MoonBit Core
+
+Welcome to the MoonBit Core repository! This document provides essential guidelines for AI coding agents to be productive and effective contributors to this codebase.
+
+## Project Overview
+MoonBit Core is the standard library for the MoonBit language. It is organized into modular packages, each with its own directory. Key files include:
+- `moon.pkg.json`: Defines package dependencies.
+- `.mbti` files: Generated interfaces for packages, providing a formal description of their public API.
+- `.mbt` files: Core implementation files, organized in block style with `///|` separators.
+- `_test.mbt` and `_wbtest.mbt`: Blackbox and whitebox test files, respectively.
+
+The top-level `moon.mod.json` file contains metadata about the entire module.
+
+## Key Workflows
+1. **Code Formatting and Interface Updates**:
+   - Use `moon fmt` to format code.
+   - Run `moon info` to update `.mbti` files. If no changes occur, your modifications are safe for external users.
+
+2. **Testing**:
+   - Run `moon test` to execute tests.
+   - Use `moon test --update` to update snapshots when behavior changes.
+   - Analyze test coverage with `moon coverage analyze > uncovered.log`.
+
+3. **Linting**:
+   - Use `moon check` to ensure code adheres to linting rules.
+
+## Project-Specific Conventions
+- **Block Style Organization**: Code blocks are separated by `///|`. The order of blocks is irrelevant, allowing independent processing.
+- **Deprecated Code**: Place deprecated blocks in `deprecated.mbt` files within the respective directory.
+- **Testing Practices**: Prefer `inspect` for snapshot testing. Use `assert_eq` sparingly, such as in loops with variable snapshots.
+
+## Integration Points
+- **External Dependencies**: Defined per package in `moon.pkg.json`.
+- **Cross-Component Communication**: Interfaces are formalized in `.mbti` files, ensuring clear boundaries between packages.
+
+## Examples
+- **Adding a New Function**:
+  1. Implement the function in a `.mbt` file, using `///|` to separate blocks.
+  2. Update the corresponding `.mbti` file with `moon info`.
+  3. Write tests in `_test.mbt` or `_wbtest.mbt`.
+  4. Format and lint the code with `moon fmt` and `moon check`.
+
+- **Refactoring**:
+  1. Modify code block by block.
+  2. Ensure no unexpected changes in `.mbti` files after running `moon info`.
+  3. Verify tests pass and update snapshots if needed.
+
+## Additional Notes
+- Refer to `AGENTS.md` for more detailed refactoring tips.
+- Use `agent-todo.md` for small, AI-friendly tasks.
+
+By following these guidelines, AI agents can contribute effectively to the MoonBit Core project. If any section is unclear or incomplete, please provide feedback for improvement!

.github/instructions/interface.instructions.md

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+---
+applyTo: **/pkg.generated.mbti
+---
+
+# MoonBit Interface File
+
+`pkg.generated.mbti` contains the public API surface for the current package.
+
+- Execute `moon info` to sync all the interface files with the actual code in the project.
+- Any change of the interface files, which reflects the change of the API, should be reviewed carefully.

.github/instructions/package.instructions.md

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+---
+applyTo: **/moon.pkg.json
+---
+
+# MoonBit Package File
+
+`moon.pkg.json` is the package manifest file for the MoonBit project. It contains metadata about the package, including dependencies, and other configuration options.
+
+[Reference]: https://docs.moonbitlang.com/en/latest/toolchain/moon/package.html

.github/instructions/readme.instructions.md

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+---
+applyTo: "**/README.mbt.md"
+---
+
+# Documentation writing guidlines
+
+`README.mbt.md` is the documentation whose MoonBit code snippets will be checked and tested.
+
+- It should be written from the aspect of the user of the API.
+- Write actual code. Do not write pseudocode in MoonBit code blocks.