Refactor CbcSolver logging with MDC context and fluent SLF4J

[dwr-bli]

Summary

This PR refactors logging in CbcSolver to improve observability and log consistency.

Changes

• add MDC context tagging for CBC solver logs
• add helper methods to set/clear solver MDC
• wrap key entry points with try/finally to ensure MDC cleanup
• migrate logger calls to fluent SLF4J style
• use structured exception logging with setCause(e)

Notes

• no intended solver algorithm change
• core modeling / solving / warm-start / IIS logic remains the same
• this is mainly a logging and maintainability improvement

[sonarqubecloud]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)
9.0% Duplication on New Code (required ≤ 3%)
C Reliability Rating on New Code (required ≥ A)
B Maintainability Rating on New Code (required ≥ A)

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[dwr-zroy]

After discussion with @dwr-bli, we have decided that #246 is sufficient to address the logging needs for now. Closing.