Improve the "tracer"

[henti]

Based on, but not limited to, Linux work:

• Raise the inotify directory count limit when needed (probably not on self-hosted runners).
• Have a fallback when we reach the inotify directory count limit. Should that be strace or C library interception?
• Handle inotify queue overflow (IN_Q_OVERFLOW).
• The list of touched files should only contain files in the repo. Otherwise we risk using unbounded space.