fix(esp32): resolve guarded framework libraries

[zackees]

Closes #1452.
Related: FastLED/FastLED#4482.

What changed

• give ESP32 framework-library discovery the compiler's ordered core/variant/SDK/project include path
• preserve header-derived macros as undecidable while collecting source-local defines, preventing conditional fallbacks in one seed from incorrectly pruning another translation unit
• retain selective per-library archives; unused framework libraries remain uncompiled/unlinked, avoiding Matter global-constructor retention without relying on LTO
• bump the LDF cache semantic version
• isolate a pre-existing QEMU runtime cache test exposed by the full suite

Validation

• bash test
• soldr cargo clippy --workspace --all-targets -- -D warnings
• focused header-scanner and SDK-capability tests
• ignored real ESP32-C6 integration test: guarded LittleFS selects both LittleFS and transitive FS
• exact FastLED production repro with this local fbuild: AutoResearch on ESP32-C6 succeeded (2.34 MB flash, 74.98 KB RAM)
• compiler-order shadow-header regression

Architecture decision

Compiling/linking every bundled ESP32 framework library is not safe: some bundled libraries are incompatible with a target, expensive to compile, or contain global constructors that can retain large subsystems. Ordinary per-library archives plus --gc-sections already provide non-LTO stripping for unreferenced members. The general solution is therefore accurate direct/transitive discovery using the compiler's include view, not a full PlatformIO LDF clone and not blanket archive inclusion.

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📥 Commits

Reviewing files that changed from the base of the PR and between 0cdeaa5 and f2689bf.

⛔ Files ignored due to path filters (1)

• ci/platform_boundary_research.tsv is excluded by !**/*.tsv

📒 Files selected for processing (10)

• crates/fbuild-build-engine/src/framework_libs.rs
• crates/fbuild-build-engine/src/framework_libs_tests.rs
• crates/fbuild-build-esp/src/esp32/orchestrator/build.rs
• crates/fbuild-build/tests/esp32_build.rs
• crates/fbuild-header-scan/src/lib.rs
• crates/fbuild-header-scan/src/scanner.rs
• crates/fbuild-header-scan/src/scanner_tests.rs
• crates/fbuild-library-select/src/cache.rs
• crates/fbuild-library-select/src/lib.rs
• crates/fbuild-toolchain/src/toolchain/esp_qemu_runtime.rs

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