feat(tck): implement updateContract JSON-RPC method

**Problem**

The TCK server does not implement `updateContract`, so the TCK driver's `ContractUpdateTransaction` suite cannot run against the Python SDK. The SDK transaction already exists: `src/hiero_sdk_python/contract/contract_update_transaction.py` (`ContractUpdateTransaction`).

**Blocked by #2594 (`createContract`)** — it creates `tck/param/contract.py` / `tck/handlers/contract.py`, and this suite needs a contract to update.

**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 an `UpdateContractParams` dataclass to `tck/param/contract.py` per the spec table (`contractId` plus the updatable fields: admin key, auto-renew settings, memo, staking fields, max automatic token associations, decline staking reward, `commonTransactionParams`).
- [ ] Add an `updateContract` handler registered via `@rpc_method("updateContract")`. Only call a setter when the param is present — a partial update must not rewrite fields the caller didn't send (see the `updateToken` / `updateTopic` handlers for the pattern).
- [ ] Add unit tests under `tests/tck/`, then run the TCK driver's ContractUpdateTransaction suite locally.

**Acceptance criteria**

- [ ] `updateContract` registered and dispatchable
- [ ] Partial updates only touch supplied fields
- [ ] Spec error cases behave as specified (missing/invalid `contractId`, immutable contract without admin key, missing admin-key signature)
- [ ] Unit tests added and the TCK `ContractUpdateTransaction` suite passes

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