feat: add --report-chars long option and its corresponding test

[junhaoliao]

closes #14023

This change introduces a long-form CLI option --report-chars as an alternative to the existing
short -r option.

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[junhaoliao]

Hi @jakkdl , I tried parameterizing the test case as instructed. Do you mind taking a look again?

[jakkdl]

rewrote the parametrize to be slightly cleaner :)

Looking at --help I'm seeing a small discrepancy where some long options are displayed with a
= before the value and some aren't - but that's not limited to this option.

  --deselect=nodeid_prefix
  --doctest-glob=pat
  --lfnf, --last-failed-no-failures={all,none}

vs

  -r, --report-chars chars
  -c, --config-file FILE

but I don't think it really matters.

I'll merge this in a few days unless somebody pops in and notices something, thank you!