Add a source post hook

[hugsy]

Description

Add a post hook to source to automatically reload gef commands and move @register-ed new commands to being active.

TODO: figure out when posthook appeared for compat

Checklist

• My code follows the code style of this project.
• My change includes a change to the documentation, if required.
• If my change adds new code, adequate tests have been added.
• I have read and agree to the CONTRIBUTING document.

[github-actions]

🤖 Coverage update for 48a79dd 🟢

	Old	New
Commit	13a9339	48a79dd
Score	71.565%	71.565% (0)

[github-actions]

🤖 Coverage update for 48a79dd 🟢

	Old	New
Commit	13a9339	48a79dd
Score	71.565%	71.5705% (0.0055)

[Grazfather]

This (somehow) breaks my hugsy/gef-extras#99

[Grazfather]

Nevermind! It's because this change was missing #1056

[github-actions]

🤖 Coverage update for eb2f6cc 🔴

	Old	New
Commit	13a9339	eb2f6cc
Score	71.5816%	71.565% (-0.0166)

[github-actions]

🤖 Coverage update for eb2f6cc 🔴

	Old	New
Commit	13a9339	eb2f6cc
Score	71.5816%	71.5623% (-0.0193)