Fix crash when isinstance() is called with JException before JVM starts

[Thrameos]

Fixes issue #1329 where calling isinstance(obj, JException) would crash with an unhandled C++ exception when the JVM had not been started or had been shut down.

The problem occurred in PyJPClass_instancecheck() which created a JPJavaFrame without first checking if the JVM was running. This caused an unhandled JPypeException to be thrown from C++ code when users tried to wrap exceptions from failed startJVM() calls.

The fix adds a JVM running check before creating the frame, following the same pattern already used in PyJPClass_subclasscheck(). When the JVM is not running, the function now falls back to Python-only type checking.

Added comprehensive test coverage for:

• isinstance() before JVM starts
• isinstance() with non-Java objects after JVM starts
• isinstance() with actual Java exceptions

Fixes #1329

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.22%. Comparing base (3e408b0) to head (66c00c2).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1436      +/-   ##
==========================================
- Coverage   86.24%   86.22%   -0.02%     
==========================================
  Files         112      112              
  Lines       10289    10289              
  Branches     4056     4056              
==========================================
- Hits         8874     8872       -2     
- Misses        809      811       +2     
  Partials      606      606              

Files with missing lines	Coverage Δ
native/python/pyjp_class.cpp	85.82% <ø> (ø)

... and 1 file with indirect coverage changes

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[Thrameos]

@marscher simple change to prevent a raise condition that happened during exception handling.