feat(fls): ZIP layer of the .fls codec

Reader and writer ported from filius-ipad with the same path policy,
limits and error codes; DEFLATE via fflate, cut at the declared size
like Apple Compression. 54 tests: the Swift archive rejection tests,
DEFLATE edge cases, and all 23 corpus files cross-checked against
fflate.unzipSync and round-tripped.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package.json

@@ -11,7 +11,7 @@
   },
   "scripts": {
     "test": "vitest run",
-    "typecheck": "tsc -b && tsc -p packages/core/test",
+    "typecheck": "tsc -b && tsc -p packages/core/test && tsc -p packages/fls/test",
     "check": "npm run typecheck && npm run test",
     "hooks": "git config core.hooksPath scripts/hooks",
     "oracle": "tools/swift-oracle/run.sh",