Add comprehensive GitHub Copilot instructions for OpenTelemetry Rust development

[Copilot]

This PR adds detailed GitHub Copilot instructions to help developers work effectively with the OpenTelemetry Rust codebase. The instructions are based on comprehensive testing and validation of all build, test, and development workflows.

What's included

The .github/copilot-instructions.md file provides:

Setup and Dependencies

• Exact commands for installing required dependencies (protoc, Rust tools, cargo utilities)
• Validated installation procedures for cargo-hack and cargo-msrv

Build and Test Commands with Measured Timings

• Core commands with realistic timeouts: All timing data gathered from actual runs
• "NEVER CANCEL" warnings: Explicit guidance to prevent premature build cancellation
• Timeout recommendations: Based on measured performance plus safety margins

Example timing data:

• cargo check --workspace: ~1m 15s (recommend 90s+ timeout)
• ./scripts/test.sh: ~4 minutes (recommend 480s+ timeout)
• ./scripts/lint.sh: ~6 minutes (recommend 480s+ timeout)

Validation Scenarios

• Step-by-step workflows for different development tasks
• Pre-commit validation procedures
• Feature-specific testing guidance

Project Structure

• Comprehensive overview of all 13+ workspace crates
• Key directories and their purposes
• Examples directory with working sample applications

Working Examples

All examples tested and validated:

cd examples/metrics-basic && cargo run     # 6 seconds
cd examples/logs-basic && cargo run        # 4 seconds  
cd examples/metrics-advanced && cargo run  # 1 second

Validation

Every command mentioned in the instructions has been tested and validated:

• ✅ All build commands work with recommended timeouts
• ✅ All examples run successfully and produce expected output
• ✅ Integration tests run (noted existing intermittent failure)
• ✅ Documentation generation works
• ✅ MSRV verification passes

The instructions follow the requirement to "always follow the instructions and only fallback to additional search and context gathering if the information is incomplete or found to be in error."

Fixes #3159.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.6%. Comparing base (b70771a) to head (8ff3efd).

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3160     +/-   ##
=======================================
- Coverage   80.6%   80.6%   -0.1%     
=======================================
  Files        126     126             
  Lines      22195   22195             
=======================================
- Hits       17898   17894      -4     
- Misses      4297    4301      +4     

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🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.