feat: Add delegate filter param's to account_tx RPC

[PeterChen13579]

This PR adds the ability to filter account_tx results based on transaction delegation. This is useful for scenarios where one account (the delegatee) signs and submits a transaction on behalf of another account (the delegator).

New Request Parameter:

"delegate": {
     "delegate_filter": "actor" or "authorizor",
     "counter_party": "account_address" 
}

Example: If User A submits a transaction to C on behalf of B:
User B (The account holder) can query with delegate_filter: "actor" to find transactions signed by others (like User A).
User A (The signer) can query with delegate_filter: "authorizer" to find transactions they signed for others (like User B).
The counter_party field can be used in either case to filter by a specific valid address

[codecov]

Codecov Report

❌ Patch coverage is 97.70115% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/rpc/common/Validators.cpp	95.00%	0 Missing and 1 partial ⚠️
...rc/rpc/filters/impl/DelegateTransactionsFilter.cpp	95.65%	0 Missing and 1 partial ⚠️

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[PeterChen13579]

Will wait for Rippled PR to be merged first before merging this one 🫡

[Copilot]

Pull request overview

Adds delegation-aware filtering to the account_tx RPC so callers can request only transactions where the queried account participated via sfDelegate (either as the authorizer/owner or as the actor/signer), optionally constrained to a specific counterparty.

Changes:

• Introduces delegate request parameter validation/parsing (delegate_filter + optional counter_party) and threads it into AccountTxHandler.
• Implements DelegateTransactionFilter to include/exclude transactions based on sfDelegate semantics and annotates results with authorizer/actor for matched delegated txns.
• Adds unit test coverage for parsing, validation, filtering behavior, and handler integration.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/unit/rpc/RPCHelpersTests.cpp	Adds unit tests for parseDelegateType / parseDelegateFilter.
tests/unit/rpc/handlers/AccountTxTests.cpp	Adds parameter-validation and handler behavior tests for delegate filtering.
tests/unit/rpc/filters/impl/DelegateTransactionsFilterTests.cpp	New unit tests for the delegate transaction filter logic.
tests/unit/CMakeLists.txt	Registers the new filter test file in the unit test build.
tests/common/util/TestObject.hpp	Declares createDelegateBlob test helper.
tests/common/util/TestObject.cpp	Implements createDelegateBlob helper to produce delegated tx blobs.
tests/common/util/MockBackendTestFixture.hpp	Removes an unused include.
src/rpc/RPCHelpers.hpp	Declares delegate parsing helpers.
src/rpc/RPCHelpers.cpp	Implements delegate parsing helpers.
src/rpc/handlers/AccountTx.hpp	Extends handler input/spec to accept delegate and adds validator.
src/rpc/handlers/AccountTx.cpp	Applies delegate filtering in the account_tx loop and adds authorizer/actor output fields (non-binary path).
src/rpc/filters/TransactionFilter.hpp	Introduces a filter interface and FilterResult struct.
src/rpc/filters/impl/DelegateTransactionsFilter.hpp	Declares DelegateTransactionFilter.
src/rpc/filters/impl/DelegateTransactionsFilter.cpp	Implements delegation-based transaction matching.
src/rpc/common/Validators.hpp	Declares delegateValidator.
src/rpc/common/Validators.cpp	Implements delegate parameter validation (required delegate_filter, optional valid-account counter_party).
src/rpc/common/Types.hpp	Adds DelegateFilter request type.
src/rpc/CMakeLists.txt	Adds the new filter implementation to the rpc target sources.

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