fix(jsonrpc): correct TransactionResult.nonce per JSON-RPC spec

[waynercheung]

What this PR does

Corrects the nonce field in TransactionResult, the response body shared by eth_getTransactionByHash, eth_getTransactionByBlockHashAndIndex, eth_getTransactionByBlockNumberAndIndex, and the full-tx mode of eth_getBlockByHash / eth_getBlockByNumber.

Closes #6547.

Why

Per ethereum/execution-apis:

• TransactionInfo.nonce is uint (QUANTITY), pattern ^0x(0|[1-9a-f][0-9a-f]*)$ - no leading zeros; zero is 0x0.

java-tron's TransactionResult previously emitted ByteArray.toJsonHex(new byte[8]) -> "0x0000000000000000" (16 hex chars), which violates the pattern.

What changes

Field	Path	Before	After
nonce	both TransactionResult constructors	0x0000000000000000	0x0

Why Block.nonce is intentionally NOT changed

Block.nonce is bytes8 per the spec (pattern ^0x[0-9a-f]{16}$), so the existing 0x0000000000000000 is already compliant. Shortening it to 0x0 would break conformance with the bytes8 length requirement.

BlockResult.nonce is therefore left untouched and existing JsonrpcServiceTest assertions on it ("0x0000000000000000") remain valid.

Compatibility

This PR makes a minimal, surgical change: only the nonce literal value is modified. All other fields in TransactionResult retain their existing serialization, preserving byte-for-byte compatibility with current production responses.

The numeric semantics of nonce are unchanged (Long.parseLong of either value yields 0); only the string representation tightens to the spec-compliant form.

Tests

TransactionResultTest is updated to:

• Assert nonce == "0x0" in both test methods (covering both TransactionResult constructors).
• Validate nonce against the schema regex ^0x(0|[1-9a-f][0-9a-f]*)$ via a small assertQuantity helper, so any future regression that re-introduces a leading-zero form will fail the test.

Pre-submit checklist

• Single module (jsonrpc), single issue (The nonce returned by eth_getTransactionByHash is non-compliant #6547), 2 files changed
• Code style follows Google Java Style
• No debug code / temporary comments / stray TODOs
• No unsafe numeric ops introduced
• No log-level changes
• No DB schema / consensus / config changes
• No dependency upgrades
• Comments explain WHY (the spec rationale), not WHAT

[waynercheung]

After review discussion, the scope of this PR has been narrowed to only the nonce field - the change directly addressing #6547. All other fields previously modified in earlier commits (v / r / s in the unsigned-signature branch, blockHash / blockNumber / transactionIndex / gasPrice in the fallback constructor) have been reverted to their original behavior to maintain strict byte-level compatibility with current production responses.

The branch has been force-pushed to a single minimal commit. Earlier inline comments on the now-removed changes are no longer applicable; please re-review the latest state.

[halibobo1205]

LGTM

[yanghang8612]

LGTM

[bladehan1]

LGTM

[0xbigapple]

LGTM