Cardano Updates

Flake lock file updates:

• Updated input 'haskell-nix':
    'github:input-output-hk/haskell.nix/cad2645' (2026-01-03)
  → 'github:input-output-hk/haskell.nix/96631ac' (2026-02-21)
• Updated input 'haskell-nix/hackage':
    'github:input-output-hk/hackage.nix/05797dd' (2026-01-03)
  → 'github:input-output-hk/hackage.nix/0af430c' (2026-02-21)
• Updated input 'haskell-nix/hackage-for-stackage':
    'github:input-output-hk/hackage.nix/fba3874' (2026-01-03)
  → 'github:input-output-hk/hackage.nix/7309ada' (2026-02-21)
• Added input 'haskell-nix/hls-2.12':
    'github:haskell/haskell-language-server/7d983de' (2025-09-24)
• Updated input 'haskell-nix/iserv-proxy':
    'github:stable-haskell/iserv-proxy/1506051' (2025-08-15)
  → 'github:stable-haskell/iserv-proxy/91ef7ff' (2026-02-04)
• Updated input 'haskell-nix/stackage':
    'github:input-output-hk/stackage.nix/8a7333a' (2026-01-03)
  → 'github:input-output-hk/stackage.nix/8124f3d' (2026-02-21)

Remove version-forcing and use `0.cabal` whenever it exists

This commit addresses the remaining Copilot review suggestions by adding
test coverage for the new functionality introduced in PR #120.

New Tests Added:

1. Unit Tests for validateGzipFile (6 test cases)
   - ✅ Accepts valid gzip files
   - ✅ Rejects files with invalid magic bytes
   - ✅ Rejects files shorter than 2 bytes
   - ✅ Rejects empty files
   - ✅ Rejects non-existent files
   - ✅ Accepts files with correct magic bytes (validates header only)

2. Integration Test for --clean-cache Flag
   - ✅ Verifies cache is created on first build
   - ✅ Verifies --clean-cache removes and recreates cache
   - ✅ Ensures build completes successfully after cleaning

Implementation Details:

- Exported validateGzipFile from Foliage.FetchURL for testing
- Created new test module: tests/Foliage/Tests/FetchURL.hs
- Updated foliage.cabal to include:
  - New test module and dependencies
  - app/ directory in test hs-source-dirs for module access
  - Required dependencies: aeson, binary, hashable, shake, network-uri, temporary
- All 10 tests pass (6 unit + 4 integration)

Test Results:
✅ validateGzipFile: 6/6 tests pass
✅ Integration tests: 4/4 tests pass (one, --no-signatures, --write-metadata, --clean-cache)

This provides confidence that:
- Gzip validation logic works correctly and won't regress
- The --clean-cache flag operates as expected
- Cache corruption prevention features are properly tested