Add GitHub Copilot instructions for project conventions and release process

[Copilot]

Adds .github/copilot-instructions.md to give Copilot context about this repo's conventions, with particular focus on the release process which has specific requirements that aren't obvious from code alone.

What's documented

• Project overview — library purpose, Promise implementation types, minification focus
• Repo structure — monorepo layout (root vs lib/), what gets published to npm
• Build/lint/test commands — npm run lint, npm run build, npm test
• Release process — the critical rules Copilot must follow:
  • Commit message format: [Release] Increase version to x.y.z
  • Files requiring updates: both package.json files, README.md (recommended version range), CHANGELIST.md
  • CHANGELIST.md rules: preserve unreleased items verbatim, move them under a new versioned heading, append a GitHub compare link (v{prev}...v{new}), leave an empty # Unreleased section for future changes
• Coding conventions — ES5 compat target, minification-oriented design, test environments (Node 18/20/22/24, Chromium browser + worker)

[Copilot]

Pull request overview

Adds a repository-specific Copilot instruction document to capture project conventions and the release process requirements that aren’t easily inferred from the codebase.

Changes:

• Introduces .github/copilot-instructions.md describing the library purpose, monorepo layout, and key build/lint/test commands.
• Documents the expected release workflow, including files to update and CHANGELIST.md formatting rules.
• Summarizes coding/testing conventions (ES5 compatibility, minification-oriented exports, CI test environments).

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.56%. Comparing base (a7c57ba) to head (25ef0cb).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #498   +/-   ##
=======================================
  Coverage   97.56%   97.56%           
=======================================
  Files          27       27           
  Lines        1439     1439           
  Branches      337      339    +2     
=======================================
  Hits         1404     1404           
  Misses         35       35           

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[nevware21-bot]

Approved by nevware21-bot