[jdjioe5-cpu]

What

Closes #2703.

This PR adds full support for contract executables in snapshot operations:

1. snapshot create captures CAP-85 ExternalRef executables:
   • Expanded SearchInputs with contract_data_keys: HashSet<(ScAddress, ScVal)> to allow targeted filtering on specific ContractData keys.
   • When encountering a ContractExecutable::ExternalRef(external_ref), snapshot create tracks the reference entry key (external_ref.executable_owner, ScVal::ExecutableTag(external_ref.tag)) for the next search pass.
   • When matching an ScVal::ExecutableTag entry, decodes the referenced 32-byte Wasm Hash into next.wasm_hashes, ensuring the underlying ContractCode is discovered and included in the snapshot.
   • Replaced silent _ => {} wildcard with explicit, exhaustive handling for all three ContractExecutable variants (Wasm, StellarAsset, ExternalRef).
2. Offline contract spec and executable resolution:
   • Implemented snapshot inspect/resolution helpers in cmd/soroban-cli/src/commands/snapshot/inspect.rs:
     • get_contract_instance
     • resolve_external_ref_wasm_hash
     • get_wasm_from_hash
     • get_wasm_hash_for_contract
     • get_contract_wasm
     • get_contract_spec
   • Fully mirrors the RPC resolution behavior (get_spec.rs, wasm.rs) for offline snapshot analysis across StellarAsset, Wasm, and ExternalRef.
3. Tests:
   • Added unit tests in inspect.rs testing StellarAsset built-in spec extraction, direct Wasm resolution, and two-hop ExternalRef resolution (Instance -> ExecutableTag ContractData -> Wasm Hash -> ContractCode -> Bytecode/Spec).
   • Added unit test in create.rs verifying SearchInputs filtering and expansion for ExternalRef.

Why

Previously, snapshot create only handled Wasm and StellarAsset, while ExternalRef fell into a catch-all _ => {} and was silently dropped. As a result, snapshots of contracts using externally-managed executables were incomplete, missing both the reference entry and the underlying Wasm bytecode. Furthermore, there were no offline helpers to resolve contract specs or executables directly from a LedgerSnapshot.