cardano-testnet: strengthen RPC ReadGenesis test coverage

[carbolymer]

Description

Strengthens the UTxO RPC ReadGenesis integration test in cardano-testnet.

• Re-enables the initialFunds assertion (temporarily relaxed in 764a27f) and upgrades it to an exact comparison: the RPC response must match the funds embedded in the genesis file.
  The expectation prefers extraConfig.initialFunds.data, where cardano-cli create-testnet-data embeds the funds, and falls back to the legacy top-level initialFunds, so the test keeps working when a future cardano-cli moves the funds back to the top level.
• Checks the returned genesis hash against the Blake2b-256 hash of the raw Shelley genesis file bytes, replacing the previous length-only check.
• Adds an error-path check: ReadGenesis fails with FAILED_PRECONDITION when the genesis file changed since the node started.
  This check runs before the first successful call, because the server caches the parsed genesis only on success.

Stacked on #6668, merge that first.
The strengthened assertions rely on cardano-rpc 11.3 server behaviour (IntersectMBO/cardano-api#1305, resolving initial funds from sgExtraConfig), and the cardano-testnet test suite only compiles with the cardano-rpc 11.3 bump carried by #6668.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. These may include:
  • golden tests
  • property tests
  • roundtrip tests
  • integration tests
    See Running tests for more details
• Any changes are noted in the CHANGELOG.md for affected package
  • cardano-node-chairman, cardano-submit-api and cardano-testnet instead need a
    changelog fragment in <package>/.changes/, because their CHANGELOG.md is generated
    from fragments at release time. Copy _TEMPLATE.yml from that directory, or run
    nix run github:input-output-hk/cardano-dev#herald -- new
• The version bounds in .cabal files are updated
• CI passes. See note on CI. The following CI checks are required:
  • Code is linted with hlint. See .github/workflows/check-hlint.yml to get the hlint version
  • Code is formatted with stylish-haskell. See .github/workflows/stylish-haskell.yml to get the stylish-haskell version
  • Code builds on Linux, MacOS and Windows for ghc-9.6 and ghc-9.12
• Self-reviewed the diff

Note on CI

If your PR is from a fork, the necessary CI jobs won't trigger automatically for security reasons.
You will need to get someone with write privileges. Please contact IOG node developers to do this
for you.