Add logger level-prefix toggle and default to plain message output

[Copilot]

pic_logger always prepended severity labels (INFO:, VERBOSE:, etc.), which made all logs explicitly tagged with level text. This change makes plain message formatting the default and adds an opt-in switch for explicit level-prefixed output.

• Logger behavior change (default path)

  • Added internal logger state to control whether level prefixes are rendered.
  • Default is now no level prefix for both console and file output.

• New public API

  • Added logger_type%set_explicit_printing(logical) to control output style at runtime.
  • set_explicit_printing(.true.) enables LEVEL: ... formatting.
  • set_explicit_printing(.false.) (or default behavior) emits plain message format.

• Formatting pipeline update

  • Updated log-line rendering to branch on explicit-printing mode while preserving module/procedure context formatting.
  • Applied consistently across console and file sinks.

• Coverage updates

  • Updated logger content assertions for new default output.
  • Added a targeted test for toggling between plain and explicit-prefixed output in the same logger instance.

type(logger_type) :: logger

! Default: no "INFO:"/"VERBOSE:" prefix
call logger%info("startup complete", "solver", "init")

! Opt in to explicit level prefixes
call logger%set_explicit_printing(.true.)
call logger%info("startup complete", "solver", "init")
! -> INFO: solver.init: startup complete

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.29%. Comparing base (04b4d2e) to head (c0530a6).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #154      +/-   ##
==========================================
- Coverage   96.31%   96.29%   -0.02%     
==========================================
  Files          54       54              
  Lines       11724    11780      +56     
  Branches      923      925       +2     
==========================================
+ Hits        11292    11344      +52     
- Misses        432      436       +4     

Flag	Coverage Δ
unittests	96.29% <100.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/lib/core/logger/pic_logger.f90	93.42% <100.00%> (+0.88%)	⬆️
test/test_pic_logger.f90	99.37% <100.00%> (+0.25%)	⬆️

... and 2 files with indirect coverage changes

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[JorgeG94]

@copilot the new functions need testing

[Copilot]

@copilot the new functions need testing

Added/expanded tests for the new logger API in commit c0530a6.

Coverage now checks set_explicit_printing across all output shapes:

• plain message
• module-only message
• module+procedure message

and validates both default plain mode and explicit INFO:-prefixed mode.