feat: add full support for all objects in ledger_entry

[mvadari]

High Level Overview of Change

This PR adds full support (including the keylet parts) for checks, NFT offers, payment channels, and signer lists.

Context of Change

Fixes #5198

Type of Change

• New feature (non-breaking change which adds functionality)

API Impact

• Public API: New feature (new methods and/or new fields)\

Before / After

Before: checks, NFT offers, payment channels, and signer lists only had basic support, to identify the object from its hash.

After: Those objects can now also be identified from the pieces that form their keylets.

Test Plan

Tests are added and pass.

[Copilot]

Pull request overview

Adds keylet-based lookup support in the ledger_entry RPC for several ledger object types that previously only supported direct hash/index lookup, aligning behavior with the goal of supporting all object types.

Changes:

• Extend ledger_entry parsing to compute keylets for Checks, NFTokenOffers, PayChannels, and SignerLists from their component fields.
• Add/expand RPC tests to cover lookups by both hash and keylet parts, including non-existent entry cases.
• Update malformed-parameter test helpers/mappings to include newly used fields (e.g., destination).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/xrpld/rpc/handlers/LedgerEntry.cpp	Adds object-form parsing for check / nft_offer / payment_channel / signer_list to compute the correct keylet-derived ledger index.
src/test/rpc/LedgerEntry_test.cpp	Adds positive and negative coverage for the new object-form requests and updates malformed-field testing to match the expanded input types.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.8%. Comparing base (afc660a) to head (864e900).

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #6319   +/-   ##
=======================================
  Coverage     79.8%   79.8%           
=======================================
  Files          858     858           
  Lines        67757   67789   +32     
  Branches      7557    7557           
=======================================
+ Hits         54064   54096   +32     
  Misses       13693   13693           

Files with missing lines	Coverage Δ
src/xrpld/rpc/handlers/LedgerEntry.cpp	85.1% <100.0%> (+1.1%)	⬆️

... and 2 files with indirect coverage changes

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

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[Copilot]

This test expects the new error code malformedDestination for invalid payment_channel.destination. If the handler switches to an existing error code (e.g. malformedAddress) for consistency with other AccountID fields, adjust this expectation accordingly so the negative tests match the API contract.

Suggested change

	{jss::destination, "malformedDestination"},
	{jss::destination, "malformedAddress"},

[Copilot]

parsePayChannel introduces a new error code string malformedDestination for an invalid destination AccountID. This error code doesn’t appear to be used anywhere else in the codebase, while other AccountID fields in this handler consistently use malformedAddress (or malformedOwner for owner fields). Consider using an existing error code (e.g. malformedAddress) to avoid expanding the public error surface with a one-off code; update the corresponding unit test expectations if you change it.

Suggested change

	LedgerEntryHelpers::requiredAccountID(params, jss::destination, "malformedDestination");
	LedgerEntryHelpers::requiredAccountID(params, jss::destination, "malformedAddress");