feat: add argument to specify the number of jobs being used for interfile

[emjin]

In combination with changes to semgrep-proprietary, this produces a speedup for interfile runs that use both intrafile and interfile rules. Instead of running both the intrafile and interfile rules with -j 1, it runs first the intrafile rules with the default number of jobs, and then the interfile rules with a single job. This conserves memory for the interfile rules while allowing the intrafile rules to benefit from multiprocessing.

TODO: we can remove the supply chain hack that disables interfile when possible to get multiprocessing

Test plan: see corresponding semgrep-proprietary PR

[github-actions]

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[r2c-argo]

semgrep-compare-github-lkgwa results

Ran benchmark on 38 repositories

The number of findings differs for 4 repos

Whole benchmark is 1.1% slower (a bit of noise is expected)

Relative speed improvement is 0.97 on average

• 3% of scans are significantly faster
• 5% of scans are significantly slower

Relative memory improvement is 0.99 on average

[aryx]

I doubt this work given you didn't modify osemgrep.
All CLI arguents processing is now by default first done by osemgrep,
so I don't think there is a way right now to call semgrep with --interfile-jobs.
In fact the test plan does not contain such command.