Remove manual Hub clones

[szokeasaurusrex]

Manual Hub clones can cause scope leakage issues. Also, with the Hub & Scope changes (getsentry/sentry-python#2533), the SDK will no longer have a concept of a Hub, so these clones likely won't do what they were intended to do anymore.

See also: https://www.notion.so/sentry/Sentry-SDK-Custom-Code-and-why-we-Should-fix-it-932c8493c29b4bb2bf18c2fc4b729ef1?pvs=4#966901ec61a140f1a18d8f63ba9c7719

Parent issue: #56248

[szokeasaurusrex]

Following discussion with @sl0thentr0py, it appears we can only remove the Hub clone in reader.py.

[edit]: We cannot even remove the hub clone in reader.py, but we can move it, so we only make the hub clone when executing in the thread pool executor

[sl0thentr0py]

yes, for future reference, the others are all some kind of thread pool executor where you want task level isolation and not thread level (since the same thread will be reused for processing tasks), so we cannot really remove those unless we have first class thread pool integration support.