Add performance and allocation review learnings from PR #327

[rmarinho]

Adds performance and allocation review learnings from PR #327 to the reviewer skill and Copilot instructions.

Changes

.github/copilot-instructions.md

• Add Reuse buffers guidance (ArrayPool<byte>.Shared + reusable readonly byte[] fields)
• Add Document thread-safety guidance (<remarks>This class is not thread-safe.</remarks>)

.github/skills/android-tools-reviewer/SKILL.md

• Add "Prefer existing repo patterns" workflow step — grep for ArrayPool, ObjectPool, MemoryStreamPool, ProcessUtils before suggesting new infrastructure

.github/skills/android-tools-reviewer/references/csharp-rules.md

• Add Reuse hot-path buffers and Reuse loop helpers to the Performance section
• Add Document thread-safety invariants to the Code Organization section

Removed from original PR (per review feedback)

• UTF-8 string literal guidance — ReadOnlySpan<byte> works on netstandard2.0 via System.Memory
• Encoding.ASCII.GetBytes() recommendation — wrong for non-ASCII content
• "No string intermediates in protocols" — overly prescriptive
• "No stackalloc in async I/O" — already a compiler error, not a review concern

Also rebased onto main to resolve merge conflicts from PR #355 (which split review-rules.md into per-category files).

[Copilot]

Pull request overview

Updates the repository’s reviewer guidance and Copilot instructions to incorporate performance/allocation learnings from PR #327, aiming to reduce allocation-heavy suggestions and align reviews with established repo patterns.

Changes:

• Expanded review-rules.md with new performance/allocation rules (ArrayPool usage, reusable buffers, avoiding string intermediates, async/stackalloc constraints, thread-safety documentation).
• Updated SKILL.md workflow guidance to grep for existing repo patterns before proposing new infrastructure.
• Enhanced .github/copilot-instructions.md with buffer-management and thread-safety guidance, plus netstandard2.0 notes.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
.github/skills/android-tools-reviewer/references/review-rules.md	Adds new performance/allocation and thread-safety review rules, plus updated netstandard2.0 guidance.
.github/skills/android-tools-reviewer/SKILL.md	Adds workflow guidance to prefer existing repo patterns (ArrayPool/ObjectPool/ProcessUtils) before suggesting alternatives.
.github/copilot-instructions.md	Updates Copilot guidance for netstandard2.0, buffer reuse/ArrayPool, and thread-safety documentation expectations.

[Copilot]

Pull request overview

Updates the repository’s reviewer skill guidance and Copilot instructions to incorporate performance/allocation review learnings (from PR #327), with emphasis on hot-path buffer reuse and avoiding avoidable allocations in protocol code.

Changes:

• Expanded reviewer rules to include new performance/allocation guidance (ArrayPool, reusable buffers, avoiding string intermediates, async stackalloc caveat, loop helper reuse, thread-safety remarks).
• Updated the reviewer workflow to explicitly prefer existing repo patterns before proposing new infrastructure.
• Enhanced Copilot instructions with buffer reuse guidance and additional netstandard2.0 considerations.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
.github/skills/android-tools-reviewer/references/review-rules.md	Adds performance/allocation-focused review checks and thread-safety documentation guidance.
.github/skills/android-tools-reviewer/SKILL.md	Adds workflow guidance to grep for existing repo patterns before suggesting new ones.
.github/copilot-instructions.md	Adds Copilot guidance on buffer reuse and netstandard2.0 compatibility pitfalls.