feat(its!): its relayer discovery

[Foivos]

why

• Adding relayer discovery to ITS as well as using it for interchain executables

how

• Deprecated the use of the execute entrypoint on ITS nad instead using a different entrypoint for each use case of execute.
• Using discovery to point the relayer to the right entrypoint.
• Assuming an interchain executable uses a special case of discoverable to allow for discovery to figure out the accounts they need.

---

Note

Replaces ITS’s monolithic execute with discovery-driven flows (deploy/link/transfer), adds transaction discovery APIs/PDAs, a discoverable test program, and updates fixtures/harness/tests to execute via relayer discovery.

• ITS (program changes)
  • Replace generic execute with specific handlers: execute_deploy_interchain_token, execute_link_token, execute_interchain_transfer, each using validate_message.
  • Add discovery endpoint get_transaction and helpers (utils::relayer_transaction, find_interchain_executable_transaction_pda, decode_interchain_transfer_payload, executable_accounts).
  • Initialize relayer transaction PDA in Initialize and include new feature/dependency wiring (relayer-discovery).
• New discoverable program: solana-axelar-test-discoverable
  • Implements init, get_its_transaction, execute_with_interchain_token, and logs via execute; initializes its own transaction and ITS interchain-executable PDAs.
• Fixtures/Harness
  • Add relayer discovery test fixture (RelayerDiscoveryTestFixture) and relayer_execute_with_checks.
  • Update ITS test fixtures and mollusk-harness to approve/execute via discovery, auto-provision payload/payer accounts, and init required PDAs.
• Tests
  • Migrate GMP tests to discovery-driven execution; add tests for interchain-transfer with data and discoverable executables; adjust helpers accordingly.
• Dependencies/Config
  • Add relayer-discovery across crates, enable ITS no-entrypoint where needed, and minor Cargo feature updates.

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[cursor]

Bug: Test deserializes counter with wrong type

The test uses solana_axelar_test_discoverable throughout (getting counter_pda at line 104, serializing Payload at lines 108-111) but then attempts to deserialize the counter account as solana_axelar_memo::Counter instead of solana_axelar_test_discoverable::Counter. This type mismatch will cause the test to incorrectly interpret the account data or fail.