Measured 2026-10-03 (frankuser)

Found by a leak probe that used {str(k)!r:>8} in a loop. Covered now: !r and !s with a fill/align/width spec, and with a NESTED width ({name!r:>{w}}), which goes through the same spec arm.

Test: test/test_nilpy_an_fstring_conversion_takes_a_format_spec.npy, byte-identical to CPython under -dPXX_HEAP_DEBUG and on i386.

!a (ascii()) is still refused by name, as before.