Add shared warm-build fast path to Teensy orchestrator

[zackees]

Summary

• add the shared warm-build fast-path wiring to the Teensy orchestrator only
• persist and reuse Teensy build fingerprints for irmware.elf, irmware.hex, and the generated compile database
• add small Teensy-local helper tests for watch collection and compile database artifact selection

Verification

• cargo test -p fbuild-build teensy::orchestrator::tests --lib
• cargo fmt --all --check -- crates/fbuild-build/src/teensy/orchestrator.rs

Scope

This is a partial issue #121 PR for the clean remaining Teensy subtask only. It does not address AVR, RP2040, STM32, or the rest of the issue.

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📥 Commits

Reviewing files that changed from the base of the PR and between bcb4aca and 9c19e61.

📒 Files selected for processing (1)

• crates/fbuild-build/src/teensy/orchestrator.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/issue-121-teensy-fast-path

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[zackees]

Filed follow-up #157 so the fast-path cache contract gets centralized instead of being open-coded per orchestrator.

The requirement is that all cache-relevant artifacts go through one shared orchestrator/pipeline contract so builders and platforms do not drift on required-artifact lists, fingerprint persistence, or side outputs like compile databases.