feat(library-selection): #205 Phase 4 zccache K/V memoization (#212)

Adds the cache module that wraps `crate::resolve` in a blake3-keyed
`zccache_artifact::KvStore` lookup, completing Phase 4 of #205. The
resolver is a pure function of (project sources, search paths, library
set, toolchain triple, framework version, scanner/LDF semantics); cold
cost is tens of ms, restore from a hit is sub-ms.

Cache key composition follows Q9 from the issue:
- sorted (canonical_path, blake3(content)) pairs for seeds,
- sorted (lib_name, blake3(canonical header)) pairs for libraries,
- ordered search-path list (order is observable per PIO semantics),
- toolchain triple, framework install path + version,
- SCANNER_VERSION + LDF_MODE_VERSION constants for invalidation.

Corrupt entries fall through to recompute and overwrite rather than
propagating decode errors — a stale cache must never poison a build.

Tests (16/16 passing):
- 9 resolver tests for the 2-pass LDF + path-prefix attribution
- 7 cache tests covering miss-then-hit, content/toolchain/version
  invalidation, input-order normalization, search-path order
  observability, and corrupt-entry recovery

Wires the workspace to `zccache-artifact = "1.4.0"` (released from
~/dev/zccache as part of the Phase 4 coordination).

Refs: #205 Phase 4

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: zackees

Cargo.lock

@@ -63,6 +63,8 @@ mimalloc = "0.1"
 object = { version = "0.36", default-features = false, features = ["read", "std", "elf", "write"] }
 rusqlite = { version = "0.31", features = ["bundled"] }
 shell-words = "1"
+bincode = "1"
+zccache-artifact = "1.4.0"
 
 # Process containment: all subprocess spawns the daemon performs (compilers,
 # esptool, qemu, simavr, node, npm, …) and any grandchildren they fork must

Cargo.toml

@@ -11,6 +11,10 @@ fbuild-header-scan = { path = "../fbuild-header-scan" }
 fbuild-packages = { path = "../fbuild-packages" }
 tracing = { workspace = true }
 walkdir = { workspace = true }
+serde = { workspace = true }
+bincode = { workspace = true }
+blake3 = { workspace = true }
+zccache-artifact = { workspace = true }
 
 [dev-dependencies]
 tempfile = { workspace = true }