Skip GNU numfmt.pl tests not yet supported: unit-sep-22-fail, grp-1,
grp-2, delim-7, field-1, field-range-err-{1-4,6-13}, strtod-6,
strtod-6.1, leading-4, debug-2, devdebug-{1-7,9-11}, help-1,
fmt-err-9, fmt-err-11, fmt-15, ign-err-5, ign-err-m2.2, ign-err-m3.1.

Also unconditionally refresh binary symlinks to avoid stale builds.

…alidation

Fixes GNU numfmt.pl tests: grp-1, grp-2, debug-2, fmt-err-9,
fmt-err-11.

Buffer formatted output so that --invalid=fail does not duplicate lines
on error, and --invalid=abort streams directly for partial output.

Fixes GNU numfmt.pl test: field-3. Re-enables the full numfmt.pl test
suite by removing the skip list added earlier in the stack.

Build the grouped string in a single forward pass using chunk iteration
instead of reversing, inserting separators, then reversing again. This
avoids an extra String allocation and collection.

Remove the trivial single-use helper and simplify split_next_field into
a compact 4-line function.

The two match arms for length 1 and length 2 had identical
RawSuffix::try_from checks. Unify into a single check after a boolean
guard.

Flatten the nested block scope by moving the output trait object and
format dispatch to the same level, reducing indentation.

Use the existing print_warning helper for the grouping-no-effect
message instead of a one-off writeln with util_name(). Use hardcoded
"numfmt:" prefix for the failed-to-convert message to match the other
debug warnings. Remove now-unused util_name import.

…o format_and_write

GNU test: numfmt.pl fmt-15

GNU test: numfmt.pl unit-sep-22-fail

GNU test: numfmt.pl devdebug-*, help-1, field-1, field-range-err-*

… and apply_grouping