feat(tck): implement contractGetBytecode JSON-RPC method

**Problem**

The TCK server does not implement `contractGetBytecode`, so the TCK driver's `ContractByteCodeQuery` suite cannot run against the Python SDK. The SDK query already exists: `src/hiero_sdk_python/contract/contract_bytecode_query.py` (`ContractBytecodeQuery`).

**Blocked by #2594 (`createContract`)** — it creates the contract-service TCK modules, and this suite needs a deployed contract to query.

**Before you start — required reading**

TCK handlers are contract work: the TCK driver validates exact parameter names, optionality, defaults, and error semantics against the published spec. Please do not code from this issue title alone (or paste it into an AI tool and ship the first thing that runs) — read these first:

1. **The spec page linked below**, in full — especially the parameter table, the expected response shape, and the error/edge-case tests. If your handler's behavior differs from the spec table, the TCK suite will fail even if the happy path works.
2. [`tck/README.md`](https://github.com/hiero-ledger/hiero-sdk-python/blob/main/tck/README.md) — how the JSON-RPC server, param dataclasses, handler registry, and responses fit together, and how to run the TCK driver locally against your handler. Run the actual TCK suite before opening a PR; unit tests alone are not enough.
3. **An existing handler as your pattern** — pick the closest one in `tck/handlers/` with its matching `tck/param/` dataclass and follow its structure, naming, and error handling exactly. Do not invent a new style, and do not re-implement SDK logic in the handler — handlers only wire validated params onto the existing SDK transaction/query.
4. **The SDK class you are wrapping** (path in the Problem section) — read its setters and defaults so you know what the SDK already handles for you.
5. [`CONTRIBUTING.md`](https://github.com/hiero-ledger/hiero-sdk-python/blob/main/CONTRIBUTING.md) — test and PR conventions.

**Solution**

- [ ] Add a `ContractGetBytecodeParams` dataclass to `tck/param/contract.py` (`contractId`).
- [ ] Add a `contractGetBytecode` handler registered via `@rpc_method("contractGetBytecode")`, returning the bytecode serialized exactly as the spec specifies (check hex vs base64 in the spec — don't assume).
- [ ] Add unit tests under `tests/tck/`, then run the TCK driver's ContractByteCodeQuery suite locally.

**Acceptance criteria**

- [ ] `contractGetBytecode` registered and dispatchable
- [ ] Returned bytecode matches the deployed contract's runtime bytecode in the spec's encoding
- [ ] Spec error cases behave as specified (missing/invalid/non-existent `contractId`)
- [ ] Unit tests added and the TCK `ContractByteCodeQuery` suite passes

Spec: https://github.com/hiero-ledger/hiero-sdk-tck/blob/main/docs/test-specifications/contract-service/ContractByteCodeQuery.md
JS reference: https://github.com/hiero-ledger/hiero-sdk-js/blob/main/tck/methods/contract.ts (`contractByteCodeQuery`)