macho: make input object file descriptors short-lived

[kubkon]

This avoids issue described in ziglang/zig#18827

Incidentally improves time performance:

Benchmark 1: ./zld
  Time (mean ± σ):      5.896 s ±  0.031 s    [User: 4.228 s, System: 2.626 s]
  Range (min … max):    5.849 s …  5.950 s    10 runs

Benchmark 2: ./zld_old
  Time (mean ± σ):      7.126 s ±  0.260 s    [User: 4.854 s, System: 3.238 s]
  Range (min … max):    6.954 s …  7.632 s    10 runs

Summary
  ./zld ran
    1.21 ± 0.04 times faster than ./zld_old

at the cost of somewhat increased memory pressure: at 1459MB up from 1156MB.

I think this tradeoff is worth it, but happy to hear opinions.

EDIT: measurements taken on Intel MBP running macOS 13.6 with 8-core [email protected] and 32GB RAM.

EDIT2: On M1Pro MBP with 32GB RAM, 1466MB up from 1192MB, while benchmarks are:

Benchmark 1: ./zld
  Time (mean ± σ):      2.559 s ±  0.008 s    [User: 2.580 s, System: 0.778 s]
  Range (min … max):    2.548 s …  2.574 s    10 runs

Benchmark 2: ./zld_old
  Time (mean ± σ):      3.064 s ±  0.007 s    [User: 2.792 s, System: 1.067 s]
  Range (min … max):    3.050 s …  3.077 s    10 runs

Summary
  ./zld ran
    1.20 ± 0.00 times faster than ./zld_old

[kubkon]

Not sure how to reason about the memory value reported by tracy - I think it may include allocations done by itself in total memory usage which perhaps I should subtract from those values.

[kubkon]

Superseded #108