test: compare integers with arbitrary precision

[mistaste]

Summary

Fixes #12874.

GNU test compares integers of any magnitude, but uutils parsed the operands of
the integer relational operators into i128 and rejected anything larger:

$ test 1 -eq 16267277278126277227728782172782882627278282882172762677623672762783782
test: invalid integer '16267277278126277227728782172782882627278282882172762677623672762783782'
$ # GNU prints nothing and exits 1

Change

• Parse the operands of -eq/-ne/-lt/-le/-gt/-ge as
  num_bigint::BigInt instead of i128. num-bigint is already a workspace
  dependency (used by expr), and the existing trimming / sign handling is
  preserved — only the artificial 128-bit range limit is removed.
• The previously #[ignore]d test_values_greater_than_i64_allowed now passes,
  so the attribute is dropped.
• Add test_arbitrary_precision_integers (CLI) and
  test_integer_op_arbitrary_precision (unit) covering values beyond 128 bits,
  including negatives.

$ test 16267277278126277227728782172782882627278282882172762677623672762783782 \
       -eq 16267277278126277227728782172782882627278282882172762677623672762783782
$ echo $?
0

Checks

• cargo test -p uu_test --lib and the test_test integration tests pass
• cargo fmt clean, cargo clippy -p uu_test --all-targets clean

[oech3]

I think we should parse letters directly.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/cut/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/rm/isatty (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/tail/tail-n0f is now being skipped but was previously passing.