testsuite: Use small allocation area when measuring residency

As suggested in #17387; this helps reduce the variance in our residency
sampling.

Metric Increase:
    T10370
    T3586
    lazy-bs-alloc

Metric Decrease 'compile_time/peak_megabytes_allocated':
    T1969

Metric Decrease 'runtime/bytes allocated':
    space_leak_001

Metric Increase 'compile_time/bytes allocated':
    T1969

Metric Increase 'runtime/peak_megabytes_allocated':
    space_leak_001

Metric Decrease:
    T3064
    T9675