Update unit tests for writing process

[rhaegar325]

Add memory validation to write() method and corresponding unit tests.

Changes

Memory Validation in write()

• Estimate data size before loading with 1.5x overhead factor
• Detect existing Dask client and check cluster memory limits
• Raise MemoryError with helpful message when data exceeds available memory
• Auto-close Dask client when data exceeds single worker memory but fits in system memory
• Gracefully handle missing dask.distributed package (lazy import)

Unit Tests

• Add TestCMIP6CMORiserWrite class covering:
  • Missing attribute validation
  • System memory checks
  • Dask cluster memory checks
  • Output file format and structure
  • Logging output

Memory Check Logic

Condition	Action
Data > total cluster memory	Raise MemoryError
Data > worker memory, < cluster total	Close client, use local memory
Data > system available memory	Raise MemoryError
Data < available memory	Proceed with write

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

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  Misses          ?      914           
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