Add purged state for debuginfo cleanup

[brancz]

This commit introduces a new STATE_PURGED state to track debuginfo that has been cleaned up from storage. This allows the system to:

1. Signal to users that debuginfo existed but was purged/cleaned up
2. Allow re-uploading of purged debuginfo
3. Prevent symbolization attempts with purged debuginfo

Changes:

• Add STATE_PURGED enum value to proto definition
• Update generated Go and TypeScript code
• Add MarkAsPurged method to ObjectStoreMetadata
• Handle purged state in ShouldInitiateUpload (allows re-upload)
• Handle purged state in symbolizer (returns ErrDebuginfoPurged)
• Add ErrDebuginfoPurged error definition

[CLAassistant]

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[alwaysmeticulous]

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