Limit the number of threads (fix memory usage)

[aminya]

↪️ Pull Request

See this comment for the analysis behind this PR.

Fixes #5072
Fixes #4628

💻 Examples

Parcel does not utilize all the threads it spawns so there is no point in using long-lived workers when they do not do anything. This results in huge memory usage and slow-down.

For example, here as you see, other than workers 0 and 1, the others almost do nothing.

🚨 Test instructions

✔️ PR Todo

• Added/updated unit tests for this change
• Filled out test instructions (In case there aren't any unit tests)
• Included links to related issues/PRs

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[aminya]

@mischnic @devongovett As I mentioned in this comment, using workers has no measurable benefits. However, if we want to keep that discussion open, I can move the limiting part to another PR, and in this PR I just fix the correct core number detection for Windows. This core number detection should fix the linked issues on windows.

[mischnic]

I can move the limiting part to another PR, and in this PR I just fix the correct core number detection for Window

Please do that