refactor: extract duplicate contract client init to _make_contract_client helper

[dataCenter430]

The same 3-line block — bt.Wallet, bt.Subtensor, IssueCompetitionContractClient(...) — was copy-pasted identically across 6 admin commands and 2 vote commands (8 sites in total). Extracting it as _make_contract_client() in helpers.py gives a single source of truth.

The lazy imports (bittensor, IssueCompetitionContractClient) are preserved inside the helper, so ImportError still propagates to the existing except ImportError handlers in each caller unchanged.

• Pyright clean
• Ruff lint and format clean

[dataCenter430]

Hi, @anderdc
admin.py has 6 commands and vote.py has 2 commands that all start with the same 8-line block — create a wallet, a subtensor, and an IssueCompetitionContractClient.
This PR extracts that block into _make_contract_client() in issue_commands/helpers.py and replaces all 8 call sites with a single line.
Really hope your review with this.

[anderdc]

Clean mechanical refactor. All 8 call sites updated, lazy imports correctly preserved, and the two sites in mutations.py that look similar were reasonably excluded (extra steps that don't fit the helper signature).

LGTM