fix: use prefixFor for BoolWithInverseFlag names and aliases

[dualfroz]

What type of PR is this?

• bug

What this PR does / why we need it:

BoolWithInverseFlag.String picks - or -- with len(name) == 1, which counts bytes. the rest of the library uses prefixFor (docs.go), which counts runes, so a one-character non-ascii name or alias is shown as --ü in the help of a BoolWithInverseFlag and as -ü for any other flag.

• flag_bool_with_inverse.go: use prefixFor for the name and for each alias.
• flag_bool_with_inverse_test.go: two cases in TestBoolWithInverseString with ü as the name and as an alias.

Which issue(s) this PR fixes:

NONE

related #2448 (same alignment for flag suggestions)

Testing

the new cases fail without the change (--[no-]ü, --[no-]color, --ü) and pass with it. go test ./..., go test -tags urfave_cli_no_template ./... and go vet ./... pass. no exported api change, godoc-current.txt unchanged.

Release Notes

BoolWithInverseFlag help now shows one-character non-ASCII names and aliases with a single dash, like other flags.

[greptile-apps]

Confidence Score: 5/5

[Medium risk] Refactors flag prefix logic to use a shared helper.

The PR appears safe to merge.

Summary

The PR makes BoolWithInverseFlag use the library’s rune-aware prefix selection for names and aliases, with tests for one-character non-ASCII values.

_{Reviews (1) · Last reviewed commit: "fix: use prefixFor for BoolWithInverseFl..." · Reviewed by Greptile}

[Juneezee]

LGTM, thanks. The two new cases fail without the change and pass with it, and the help output now matches other flags:

GLOBAL OPTIONS:
   -[no-]ü           (default: false)
   --[no-]color, -é  (default: false)
   -ä

I pushed one more commit for the same mismatch in the "cannot set both flags" error, which still hardcoded -- for the name. With Name: "e", -e --no-e failed with cannot set both flags `--e` and `--no-e` ; it now says -e, with a test for e and ü