Add test suite for block ref rewrite

[rekmarks]

Explanation

The block-ref-rewrite middleware lacked a dedicated test suite, making it difficult to verify its behavior and prevent regressions. This PR introduces a comprehensive test suite for createBlockRefRewriteMiddleware.

The new tests cover:

• Error handling for missing blockTracker dependency.
• Scenarios where block reference rewriting should be skipped (e.g., methods without block reference parameters, non-"latest" block references).
• Core functionality, ensuring "latest" block references are correctly rewritten to actual block numbers for various RPC methods (eth_getBalance, eth_getStorageAt, eth_getBlockByNumber).
• Edge cases, such as handling omitted block references (which should default to "latest") and non-array parameters.
• Verification that other request properties remain unchanged during the rewrite process.

The tests utilize JsonRpcEngine and a mock PollingBlockTracker to simulate realistic usage and assert the middleware's impact on RPC requests.

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

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