[#noissue] Lower log level for missing classes in ASMClassWriter

[Dongnyoung]

Hello,

Background

While testing Pinpoint in a real Spring Boot application, I observed that
ASMClassWriter logs WARN messages when optional classes are missing.

Problem

This is a normal fallback path, but logging it as WARN produces noisy logs
and may mislead users into thinking there is a problem.

Change

Lower the log level from WARN to DEBUG without altering behavior.

Verification

Reproduced by attaching the Pinpoint agent to a Spring Boot application.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 33.18%. Comparing base (55c9a25) to head (bb8e6c4).
⚠️ Report is 26 commits behind head on master.

Files with missing lines	Patch %	Lines
...p/pinpoint/profiler/instrument/ASMClassWriter.java	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #13281      +/-   ##
============================================
- Coverage     33.21%   33.18%   -0.03%     
- Complexity    10968    10972       +4     
============================================
  Files          4062     4070       +8     
  Lines         94305    94441     +136     
  Branches       9823     9830       +7     
============================================
+ Hits          31326    31343      +17     
- Misses        60306    60424     +118     
- Partials       2673     2674       +1     

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[Dongnyoung]

This change only adjusts the log level (warn → debug) and does not affect runtime behavior.
The missing coverage comes from a null-check branch that is not exercised by existing tests.
Please let me know if you’d prefer a different approach or additional tests.