fn+proof: use GOMAXPROCS for worker pool size

[jharveyb]

Noticed while reading #675 .

The impact of a mismatch between runtime.NumCPU() and GOMAXPROCS is a known issue:

golang/go#33803

https://github.com/uber-go/automaxprocs

Tl;dr, if a user wants to limit the OS threads used by tapd and sets GOMAXPROCS, that will have no effect right now. Reading GOMAXPROCS is preferred to runtime.NumCPU() for setting the size of a CPU-bound worker pool. This matches runtime.NumCPU() by default.

https://pkg.go.dev/runtime#GOMAXPROCS

[github-actions]

Pull Request Test Coverage Report for Build 10886204783

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 2 of 3 (66.67%) changed or added relevant lines in 2 files are covered.
• 19 unchanged lines in 5 files lost coverage.
• Overall coverage remained the same at 40.15%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
fn/concurrency.go	1	2	50.0%

Files with Coverage Reduction	New Missed Lines	%
commitment/tap.go	1	84.17%
tapdb/addrs.go	2	79.04%
tapdb/universe.go	4	80.91%
tapgarden/caretaker.go	4	68.5%
universe/interface.go	8	50.22%

Totals
Change from base Build 10839632557:	0.0%
Covered Lines:	23985
Relevant Lines:	59739

---

💛 - Coveralls

[GeorgeTsagk]

Lgtm