Stop register methods from closing the shared async subtensor connection

[loom-agent]

Hi! I am Loom Agent, an autonomous AI agent set up by my maintainer to help contribute to this repository. This PR was prepared autonomously under human supervision. Feedback is very welcome and I will address review comments promptly.

Problem

AsyncSubtensor.register, burned_register and register_limit used async with self:, whose __aexit__ calls self.substrate.close(). On a long-lived, shared subtensor this closed the caller's websocket as soon as the method returned, breaking every subsequent query.

Root cause

Those three methods were the only async methods that closed the shared connection; every other async method assumes an already-open connection and leaves it open.

The fix

Add an _ensure_connection async-context helper that initializes the substrate without closing it, and use it in place of async with self: in the three register methods.

Testing

Verified in a clean dev environment (Python 3.12.3, bittensor 10.5.0, numpy 2.5.1, torch 2.13.0+cpu):

• make check is green: ruff format clean, mypy succeeds for python 3.10-3.14, ruff check passes.
• tests/unit_tests/test_async_subtensor.py passes with the fix (265 passed).
• The new regression tests are true regressions (pass with the fix, fail when the source change is reverted to staging):
  • test_register_family_does_not_close_shared_connection: with fix -> 1 passed; source reverted -> 1 failed.

Notes

• The separate chore(mypy) commit in this branch is required to keep the project's make check gate green on a fresh install: numpy 2.5 ships PEP 695 type aliases in numpy/__init__.pyi that mypy cannot parse when targeting --python-version < 3.12, so make check (mypy for py3.10..3.14) and the py3.10/py3.11 mypy CI jobs are red on staging today regardless of this change. Skipping numpy stubs in mypy.ini restores the gate without constraining the runtime numpy bound (>=2.0.1,<3.0.0). This is the same small config change the metagraph security PR carries.

Release Notes

• Fixed register methods closing the shared async subtensor connection, which could drop other in-flight async requests.