`util.getManifest` is very expensive and can balloon memory usage.

[agc93]

Describe the bug
Testing for #8663 eventually led me to the major contributor of the slowdown and memory consumption: util.getManifest. This isn't strictly a bug, but might be worth just noting in the tsdoc for the function so that no-one else makes this mistake.

Calling util.getManifest is quite expensive: on my machine it takes 150-200ms per call, and since there's a call to Buffer.toString somewhere in there, it can also cause a huge allocation of memory if called repeatedly. In my case, I was stupid and was calling it per-mod and that can balloon to the point of crashing Vortex.

To Reproduce
Steps to reproduce the behavior:

1. Repeat any loop 100+ times (or 1000 if you've got a lot of RAM)
2. Call util.getManifest() every loop
3. It will be fairly slow but more importantly the heap will rapidly grow in size

Expected behavior
This isn't really a bug, just might be worth throwing a cautionary note in the tsdoc. If you really wanted, a super-short-lived cache could also avoid this, but I think that's probably a bit much for a problem that should only show up if an extension developer is doing things wrong.

Platform (please complete the following information):

• OS: Windows 10
• Vortex Version 1.4.3

[TanninOne]

Fully agree with the documentation change.
Technically we could probably cache the manifest on our end since we can track when the manifest gets updated but it does feel like one of those situations where software tries to be too smart for its own good.

Still, I'll reopen this issue and keep it open for now as a reminder, please don't expect any change to this any time soon.