Cleanup metadata flusher.

[pykello]

Several things could become simpler now that we did the big refactor in eacf337.

[greptile-apps]

Greptile Summary

This PR simplifies the MetadataFlusher implementation by replacing usize counters with boolean flags for tracking flush request states. The changes are part of a cleanup effort following a major refactor (eacf337).

Key modifications include:

• Added constants METADATA_WRITE_ID and METADATA_FLUSH_ID to replace magic numbers and improve code clarity
• Changed pending_flush_requests and inprogress_flush_requests from usize counters to bool flags, recognizing that the metadata flusher only processes one flush at a time
• Refactored the polling logic by extracting flush completion handling into a dedicated finish_flush method
• Updated the busy() method to use boolean operations instead of numeric comparisons

This change fits well with the codebase's architecture where the MetadataFlusher operates sequentially - only one metadata flush can be in progress at any given time. The boolean approach eliminates potential counting bugs and reduces complexity while maintaining the same functional behavior. The extracted finish_flush method improves code organization by centralizing flush completion logic, including proper error handling and state cleanup.

Confidence score: 4/5

• This is a safe refactoring that simplifies the code without changing functional behavior
• The score reflects solid implementation with clear improvements, though thorough testing would be beneficial
• No files need additional attention - the changes are well-contained and logical

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[Copilot]

Pull Request Overview

This PR simplifies the metadata flusher implementation by converting counters to boolean flags and refactoring the polling logic. The changes leverage simplifications made possible by a previous refactor (eacf337).

• Converted flush request counters from usize to bool since only one flush can be active at a time
• Added named constants for metadata operation IDs to improve code readability
• Refactored polling logic by extracting finish_flush method and simplifying state management