tests: add teensy30 regression coverage for local lib/FastLED shadowing bundled framework FastLED

[zackees]

Problem

We just fixed a Teensy 3.0 regression where fbuild selected the bundled Teensy framework libraries/FastLED even when the project already had a local lib/FastLED.

That produced duplicate FastLED builds and linker failures in the FastLED repo on teensy30:

• project-local copy: lib/FastLED/...
• bundled framework copy: framework-arduinoteensy/.../libraries/FastLED/...

The symptom was a long series of multiple-definition errors for CFastLED, FastLED, power_mgt, noise, palette symbols, etc.

What to add

Please add dedicated teensy30 regression coverage for this shadowing case in the Teensy test suite.

Suggested shape:

• fixture based on tests/platform/teensy30
• include a project-local lib/FastLED/ tree
• build a sketch that includes <FastLED.h>
• assert that the bundled Teensy framework FastLED is not selected/compiled when the local library exists

Good targets

Either of these is fine:

• crates/fbuild-build/src/teensy/orchestrator.rs unit coverage for framework-library selection
• crates/fbuild-build/tests/teensy_build.rs ignored integration coverage using a teensy30 fixture

The important thing is that a future regression would fail specifically on the Teensy 3.0 path, not just in downstream FastLED CI.

Why this matters

teensy30 already has a fixture under tests/platform/teensy30, but the current Teensy integration tests are centered on teensy41, so this exact 3.0 shadowing path can regress without an obvious test failure inside fbuild itself.

[zackees]

PR #198 now includes the actual fix plus the teensy30 regression coverage from this issue, so it is set up to close both #199 and #195 when merged.

PR: #198