perf(vcs): cache the hashes of untracked files when possible

[vvagaytsev]

Now Garden scans all the untracked files twice:

• While looking for Garden config files
• While actions/modules resolution

For big projects with a large amount of untracked files that can cause performance downgrade.

For non-persistent commands and commands that are running outside the fev console it seems to be possible to cache the hashes of the untracked files.

Fixes #5844

[vvagaytsev]

It's an optimization to save time on scanning projects with a large amount of untracked files. Let's double-check if this approach is reliable and there are not uncovered corner-cases left.

It should be ok to cache files in non-persistent commands and in the commands that are running outside the dev console. Is there anything related to Cloud that hasn't been taken into account in the PR?

cc @eysi09 @thsig @edvald

[edvald]

My first instinct is that this could fail in some unforeseen manner, but I'm not sure if I can think of a concrete failure mode. I wonder if we shouldn't use the TreeCache helper for this? That's what we use for other types of caching that may need to be invalidated across command runs in the same process.

I'd also consider making this opt-in via environment variable, at least while we're proving this out.