QA: add tests for eth_getHeaderByNumber() eth_getHeaderByHash()

[lupin012]

QA integration tests for eth_getHeaderByNumber and eth_getHeaderByHash, the two APIs added in #23717.

The fixtures live in erigontech/rpc-tests#603; this PR only pins RPC_VERSION to that branch so the QA workflows pick them up.

eth_getHeaderByNumber

test	param	case
01	0x41b57c	pre-London: no baseFeePerGas, no post-Merge fields
02	0xC65D40	London: baseFeePerGas set, difficulty still non-zero
03	0x1036640	post-Merge pre-Shanghai: difficulty 0x0, no withdrawalsRoot
04	0x112A880	Shanghai: withdrawalsRoot set, no blob fields
05	0x12C135B	Cancun: blobGasUsed, excessBlobGas, parentBeaconBlockRoot
06	0x1600000	Prague: requestsHash
07	earliest	resolves to the genesis header
08	latest	head header (metadata.latest, runs only with -L)
09	pending	null, the pending block is not exposed
10	0x7FFFFFFFFFFFFF	unknown number: null, not an error
11	abc	invalid number: hex without 0x prefix, error

eth_getHeaderByHash

test	case
01	pre-London: no baseFeePerGas, no post-Merge fields
02	London: baseFeePerGas set, difficulty still non-zero
03	post-Merge pre-Shanghai: difficulty 0x0, no withdrawalsRoot
04	Shanghai: withdrawalsRoot set, no blob fields
05	Cancun: blobGasUsed, excessBlobGas, parentBeaconBlockRoot
06	Prague: requestsHash
07	genesis block hash
08	unknown hash: null, not an error
09	invalid hash: wrong length, error
10	invalid hash: not a string, error

The same blocks are used by number and by hash, so the two APIs are compared on identical headers.

Integration-Tests

Compared eth_getHeaderByNumber() and eth_getHeaderByHash() for historical block automatically on QA - RPC Integration Tests / mainnet-rpc-integ-tests
Compared eth_getHeaderByNumber() output with geth on the latest block — results match. Dispatched manually: CI run.

[lupin012]

@MysticRyuujin I have added rpc-tests for the new RPC methods eth_getHeaderByNumber() and eth_getHeaderByHash() of your PR