fix: restore log flow to root logger on disable (DM-3439)

[haakonvt]

Description

https://cognitedata.atlassian.net/browse/DM-3439

In the SDK, we accept the “debug: bool = False” parameter, which also can be turned on or off later. It has 2 main issues:

1. Critical Issue: The "Silent Logger" Bug

_disable_debug_logging() leaves the logger in a broken state.

The Flow:

1. _configure_logger_for_debug_mode() sets logger.propagate = False.
2. _disable_debug_logging() clears all handlers (logger.handlers = []) but does not reset propagate to True.

The Result: After you enable and then disable debug mode, the logger has no handlers and does not propagate to the root logger. Any subsequent logs (even errors or warnings) will be silently swallowed and effectively lost.

Fix: Restore propagation in the disable function.

2. High Risk: Direct List Manipulation

Directly assigning logger.handlers = [] is generally discouraged in Python logging for two reasons:

1. Thread Safety: The logging module has internal locks. Modifying the list directly bypasses these safety mechanisms, which could cause race conditions in a multi-threaded application.
2. Destructiveness: This wipes out any handler attached to that logger. If a user had manually attached a FileHandler to the Cognite logger to save logs to a disk, this function would silently delete it.

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[codecov]

Codecov Report

❌ Patch coverage is 61.11111% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.33%. Comparing base (a2cc565) to head (90c1928).

Files with missing lines	Patch %	Lines
cognite/client/utils/_logging.py	61.11%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2429      +/-   ##
==========================================
+ Coverage   91.28%   91.33%   +0.04%     
==========================================
  Files         192      192              
  Lines       26184    26176       -8     
==========================================
+ Hits        23903    23907       +4     
+ Misses       2281     2269      -12     

Files with missing lines	Coverage Δ
cognite/client/utils/_logging.py	77.50% <61.11%> (+23.33%)	⬆️

... and 3 files with indirect coverage changes

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[haakonvt]

/gemini review

[gemini-code-assist]

Code Review

This pull request effectively addresses a critical bug where disabling debug logging would silence the logger entirely. The changes are well-implemented, replacing the unsafe direct manipulation of logger.handlers with the thread-safe addHandler and removeHandler methods, and correctly restoring log propagation. The refactoring of DebugLogFormatter is also a great improvement in simplicity and correctness. I've added a couple of suggestions to further enhance thread safety by iterating over a copy of the handlers list, which fully resolves the race condition concerns mentioned in the description.