refactor: move MAX_ISSUE_ID to gittensor/constants.py and use it on the validator side

[ebios-star]

Summary

Follow-up to the just-merged #873, which deduped the 1_000_000 issue-ID bound on the CLI side using the helpers.py-local MAX_ISSUE_ID. The validator-side path in IssueCompetitionContractClient.get_issues_by_status still carries its own local copy with the same value and same intent:

# gittensor/validator/issue_competitions/contract_client.py:194-195
MAX_REASONABLE_ISSUE_ID = 1_000_000
if next_issue_id > MAX_REASONABLE_ISSUE_ID:

This PR hoists MAX_ISSUE_ID into gittensor/constants.py (alongside CONTRACT_ADDRESS, ISSUES_TREASURY_UID, etc.) so both consumers share a single definition. Validator code stays clean of any cli/* dependency, matching the import-direction precedent already set by #425 (NETWORK_MAP) and #460 (get_contract_address).

Changes

• gittensor/constants.py — add MAX_ISSUE_ID = 1_000_000 to the Issues Competition section.
• gittensor/cli/issue_commands/helpers.py — drop the local definition, import from gittensor.constants. Existing call sites (validate_issue_id, _read_issues_from_child_storage) are unaffected.
• gittensor/validator/issue_competitions/contract_client.py — drop local MAX_REASONABLE_ISSUE_ID, import MAX_ISSUE_ID from gittensor.constants.

Net: +4 / -4 lines across 3 files. No behaviour change — same 1_000_000 bound, same comparison.

(Happy to fold this into the #955 bundle if that's preferred — easy to cherry-pick.)

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Other

Testing

• pytest tests/ — all 754 tests pass.

Checklist

• Code follows project style guidelines
• Self-review completed
• Changes are documented (if applicable)

[ebios-star]

@anderdc whenever you have a moment, this is a small follow-up to the just-merged #873 that hoists the issue-ID bound into gittensor/constants.py so the validator side can share the same constant. Happy to fold into the #955 bundle if that's preferred. Thanks!

[ebios-star]

Consolidated into #917 per @anderdc's request — closing in favour of the bundled review.