Add pre-PR requirements to run cargo fmt and clippy in agent instructions

[Copilot]

Adds explicit instructions for the Copilot agent to run rust fmt and clippy fixes before opening a pull request.

Changes Made

Added a new "Pre-Pull Request Requirements" section to .github/instructions/rust.instructions.md that instructs the agent to:

1. Format code with rustfmt: Run cargo fmt
2. Apply clippy fixes: Run cargo clippy --fix --all-targets --all-features --allow-dirty --allow-staged
3. Verify no warnings remain: Run cargo clippy --all-targets --all-features -- -D warnings

These instructions ensure code quality and consistency are enforced by the agent before a PR is opened for review, rather than relying on CI to fix issues after the PR is created.

Original prompt

The agent shouuld run rust fmt and clippy fixes before opening a pull request

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✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[becheran]

@copilot but i want the agent to do this before actually opening the pr. Can'ty you set it up as instructions file for the agent?

[Copilot]

@copilot but i want the agent to do this before actually opening the pr. Can'ty you set it up as instructions file for the agent?

Added a "Pre-Pull Request Requirements" section to .github/instructions/rust.instructions.md with explicit instructions to run cargo fmt and cargo clippy --fix before opening PRs. Commit: fb375d2