Improvement: enable inline named args

[arkjedrz]

This is currently not supported by macros, due to invalid span being used.
Right now: mw_log_format_args!("{}", x1).
Expected: mw_log_format_args!("{x1}").

Additional notes, 11.12.2025:
This is not possible to do with proc-macros nested inside declarative macros.
E.g., error! declarative macro from mw_log calls mw_log_format_args! procedural macro.
It is possible to change span inside proc macro to call site, but this means span is at declarative macro, which provides fixed mixed-site span. Created identifier is then not being able to access external variable.

One option would be to rewrite all mw_log macros to proc macros, but this might be a larger effort.