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>

packages/fls/src/encoding.d.ts

@@ -0,0 +1,12 @@
+// TextEncoder/TextDecoder exist in every target (browsers, Node, workers) but
+// belong to the DOM and Node type libraries, which this package does not load
+// on purpose. Declared here to the extent the codec uses them.
+
+declare class TextDecoder {
+  constructor(label?: string, options?: { fatal?: boolean; ignoreBOM?: boolean });
+  decode(input?: Uint8Array): string;
+}
+
+declare class TextEncoder {
+  encode(input?: string): Uint8Array;
+}