fix: cache uncompressed CRS after first decompression

[johnathan79717]

Summary

• After PR feat: SRS point compression - download 50% less CRS data #21112 switched CRS storage to compressed format (32 bytes/point), every CRS load decompresses from scratch. For 2^20 points in a browser that's ~4s on every page load; for 100M points on an 8-core native prover that's ~110s.
• This PR makes compression a bandwidth-only optimization: after the first decompression, the uncompressed points (64 bytes/point) are cached and reused on subsequent loads.

Changes

C++ native (get_bn254_crs.cpp): Check for cached bn254_g1.dat (uncompressed) first. On cache miss, decompress from bn254_g1_compressed.dat and write the uncompressed cache. On download, cache both compressed and uncompressed.

C++ WASM (bbapi_srs.hpp/cpp): srsInitSrs auto-detects input format (32B vs 64B per point). When decompressing compressed input, it returns the uncompressed bytes in the response so the caller can cache them.

Browser (cached_net_crs.ts): Check IndexedDB for uncompressed g1Data first. Add cacheUncompressed() to persist after first decompression.

Node.js (crs/node/index.ts): Check bn254_g1.dat first, fall back to bn254_g1_compressed.dat. Add cacheUncompressed() to write uncompressed file.

Wiring (barretenberg/index.ts): initSRSChonk captures the srsInitSrs response and calls crs.cacheUncompressed() when uncompressed bytes are returned.

Test plan

• C++ native: run bb with only compressed CRS on disk, verify it creates bn254_g1.dat and uses it on second run
• WASM: ./scripts/run_test.sh bbapi/exception_handling.test.js passes (schema change)
• WASM: ./scripts/run_test.sh barretenberg/blake2s.test.js passes (skipSrsInit)
• Browser: first load downloads compressed, caches uncompressed in IDB; second load skips decompression