mutate: each bounded process watched by its own ticker

[aledbf]

Follows #20, from a KISS/YAGNI review of what the repositories took at 7fefec3.

What changes

• One watcher per bounded process instead of one shared poller. The poller mutate: every test process held to its share of the memory #20 added started once and never ended, scanned /proc every 100 ms even with nothing running, and needed a registry (map, mutex, sync.Once), a watch type, and a copy of the limit in each watch, which existed only because the goroutine outlived the tests that change memLimit. Now bounded starts a goroutine that ends when Wait returns: it is born with Start and dies with Wait, with no package state. The cost is one /proc scan per process per tick: about 2 ms, a fifth of one core at -j 10, beside the ten test processes it measures.
• A loop of parents is walked once. /proc is read one process at a time, so a pid reused mid-scan can close a loop A→B→A, which the walk followed for ever while holding the lock. The walk is now treeOf, a pure function with a seen set, and a test with a loop of parents holds it.

The tests from #20 (the mutant stopped, the package as it is let be under the same bound, no test binary left running) are unchanged and pass.

task test (race), task lint and task mutate (7 refused, 0 survived) green locally.

🤖 Generated with Claude Code

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