Eagerly remove `Handle`s from the manager

[FinleyMcIlwaine]

This PR is based on #985. That should be merged first, then this can be rebased on main and merged.

Previously, if many streams were opened on a connection with a very long timeout, the handles would accumulate. This PR causes the handles to be removed from the manager immediately upon cancel, instead of relying on timeouts causing the reaper to remove them.

Before submitting your PR, check that you've:

• [x] Bumped the version number

After submitting your PR:

• [x] Update the Changelog.md file with a link to your PR

[kazu-yamamoto]

Rebased and merged. Thank you for your contribution!