Extract duplicate DILL_VERSION checks to private function and add 0.3.9 support

[Copilot]

This PR addresses code duplication in src/datasets/utils/_dill.py where the same DILL version check was repeated twice, and adds support for dill version 0.3.9.

Problem

The file contained identical version checks at two different locations:

# First occurrence (lines 118-122)
elif config.DILL_VERSION.release[:3] in [
    version.parse("0.3.6").release,
    version.parse("0.3.7").release,
    version.parse("0.3.8").release,
]:

# Second occurrence (lines 315-319) 
elif config.DILL_VERSION.release[:3] in [
    version.parse("0.3.6").release,
    version.parse("0.3.7").release,
    version.parse("0.3.8").release,
]:

This duplication made the code harder to maintain and didn't include support for dill version 0.3.9.

Solution

1. Created a private function _is_supported_dill_version() that centralizes the version checking logic
2. Added version 0.3.9 to the supported versions list
3. Replaced both duplicate checks with calls to the new function

def _is_supported_dill_version():
    """Check if the current dill version is in the supported range."""
    return config.DILL_VERSION.release[:3] in [
        version.parse("0.3.6").release,
        version.parse("0.3.7").release,
        version.parse("0.3.8").release,
        version.parse("0.3.9").release,  # ← New version added
    ]

Changes

• Eliminated code duplication: Both version checks now use the same private function
• Added 0.3.9 support: The new version is now properly handled for both logging and CodeType serialization
• Improved maintainability: Future version additions only need to be made in one place
• No functional changes: All existing behavior is preserved

The changes are minimal and surgical - only 12 lines added and 10 lines removed, with no impact on existing functionality.

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