fix(servicenow-provider): fix pagination, auth, and a NameError in notify_update

[Prabal864]

What

Fixes #6723.

Four independent bugs in keep/providers/servicenow_provider/servicenow_provider.py, all confirmed directly against the current code:

1. Pagination always returns page 1. _query's if sysparm_offset: params["sysparm_offset"] = 0 hardcoded 0 instead of forwarding the caller's sysparm_offset. _get_incidents calls _query in a while True loop, advancing offset only when a full page comes back — since every page after the first was actually still page 1, and a full page (100 items) kept coming back, this loop never terminated naturally for any instance with >= 100 incidents.
2. NameError instead of HTTPError in _notify_update's failure branch — resp.raise_for_status() where resp is only ever assigned inside the status_code == 200 branch, so the else branch always raised NameError instead of the real HTTP error.
3. Inverted auth in _notify_update — its auth-tuple construction used if self._access_token where every other auth site in this file (_query, _notify, pull_topology, _get_auth) uses if not self._access_token. This meant OAuth-configured instances got basic auth sent on ticket updates instead of (or alongside) the bearer token.
4. Missing comma in pull_topology's CMDB fields list — "owned_by.name" directly followed by "manufacturer.name", with no comma between them, so Python's adjacent string-literal concatenation silently merged them into one nonexistent field ("owned_by.namemanufacturer.name"), so the ServiceNow API never returned either value.

Testing

Added to tests/test_servicenow_provider.py:

• TestQueryPagination — asserts a non-zero sysparm_offset reaches the request unchanged, and that 0 stays 0.
• TestNotifyUpdate — asserts basic auth is used when there's no access token, the bearer header is used (and auth=None) when there is one, and the failure path raises the real HTTPError instead of crashing with NameError.
• TestPullTopologyFields — asserts owned_by.name and manufacturer.name both appear as separate entries in the requested sysparm_fields.

I wasn't able to run the suite in my sandbox for the same reason as my last PR here — this repo's ContextManager (imported transitively by the provider base classes) unconditionally pulls in keep/api/core/db.py's full dependency chain (opentelemetry, mysql-connector, etc.), and a full pip install -e . fails on Windows regardless (uvloop doesn't support it). I traced each fix by hand against the exact current code (line numbers/behavior confirmed via git show/git grep against upstream/main) and the added tests follow this file's existing MagicMock-based fixture pattern, so they should run cleanly under CI. python -m py_compile passes on both changed files.

Note: I didn't run black/isort on the full file since it isn't currently formatted with either on main and CI doesn't enforce them here — didn't want to bundle an unrelated reformat into this diff. My changed lines are minimal and match the surrounding style.