[sharkdp]

Fixes #161.

Use a blocking wait4() on Linux to collect peak RSS when the type-checker exits (the OOM watcher still uses /proc/<pid>/status for querying while the process is still running).

I ran a benchmark for each type-checker on "cerify". Each cell shows min..max peak RSS in MiB for five benchmarking runs. GNU time is used for comparison. As we can tell from this table, the new ("After") results are closed to the time measurements, especially for the fast-running type checkers. The previous implementation could miss as much as 13 MiB, or 20% of the peak RSS (see e.g. the "min" times in the Pyrefly row):

Checker	Before	After	GNU time
Pyright	141.7..142.8	141.8..142.6	141.7..142.3
Pyrefly	51.9..65.2	64.2..64.6	64.4..64.6
ty	37.6..42.6	46.9..47.4	46.9..47.5
mypy	114.7..115.4	114.7..115.1	114.6..115.4
Zuban	27.2..27.5	32.9..33.1	33.0..33.3