refactor(net): truncate oversized signatures

[Federico2014]

What does this PR do?

Follow-up to tronprotocol#6782. For transaction signatures longer than 68 bytes, truncate the trailing bytes to exactly 68 instead of rejecting the transaction. Signatures shorter than 65 bytes are no longer rejected up front — they fall through to downstream signature verification, which still rejects them.

• TransactionCapsule.sanitizeSignatures() truncates each oversized signature to 68 bytes; signatures already in range are untouched (no rebuild, no transaction-id change).
• TransactionsMessage.sanitizeSignature() sanitizes every contained transaction and rewrites the wire bytes when anything changed.
• Wallet.broadcastTransaction and TransactionsMsgHandler.check call sanitize first, then drop the now-redundant per-signature length validation.
• RelayService (peer hello handshake) keeps the strict [65, 68] check inline; SignUtils.isValidLength is removed since no caller remains.

Why are these changes required?

The strict admission filter from tronprotocol#6782 also rejects historical transactions whose signatures legitimately carry trailing padding beyond 68 bytes. Truncating those bytes preserves the canonical 65-byte r/s/v while still admitting the transaction, matching the sanitize pattern introduced in tronprotocol#6797.

This PR has been tested by:

• Unit Tests
  • new SanitizeSignaturesTest (capsule + message-level, 8 cases)
  • updated WalletMockTest.testBroadcastTxInvalidSigLength
  • updated TransactionsMsgHandlerTest.testInvalidSigLength
• ./gradlew :framework:checkstyleMain :framework:checkstyleTest

Follow up

None.

Extra details

Peer hello handshake (RelayService) intentionally stays strict — hello signatures are not on the transaction admission path and have no historical padding to accommodate.

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Summary by cubic

Truncate transaction signatures longer than 68 bytes at admission instead of rejecting them to restore compatibility with historical transactions. Upfront length checks are removed; undersized signatures still fail during downstream verification.

• Refactors
  • Add sanitize in TransactionCapsule to trim each signature to 68 bytes; in-range signatures are untouched and txid stays the same.
  • Add sanitize in TransactionsMessage and rewrite wire bytes only when changed.
  • Call sanitize in Wallet.broadcastTransaction and TransactionsMsgHandler; remove redundant per-signature length checks.
  • Keep strict [65, 68] check in RelayService hello; remove SignUtils.isValidLength.

^{Written for commit 6ff34e6. Summary will update on new commits. Review in cubic}

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No issues found across 9 files

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