fix: assets copying from 'nest build' is problematic

[NikolaPeevski]

PR Checklist

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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
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PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Other... Please describe:

What is the current behavior?

Currently the closeWatcher executes midway of copying assets. Very notisable in a file structure with a lot of subfolders/files.

Issue Number: #1117

What is the new behavior?

Refactored closeWatchers to check if a recent action has been exectued in order to reduce race conditions and reset the timer. Additional timeout will trigger repeating the process until a recent action has not been executed, at which it will close the watchers.

Note: The race condition could still be a problematic factor when copying bigger files, I'd assume, for which a more clever/robust solution should be applied. Additionally the timeout of 300 was increased to 500 to lessen the timeout spam on the event loop. Could be increased further upon analysing or set dynamically based on file sizes/files count ratio to reduce spam.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

This was a pickle to investigate. Good find.

[kamilmysliwiec]

LGTM