Config/metadata actions: UpdateConfig, UpdateTableMetadata, SetDataFormat, SetFeatureFlags, ReserveFragmentIds (internal)

[wjones127]

Parent PRD

Milestone: Action-based Transactions (UserOperation) — see milestone description for full PRD.
Discussion: #5960

What to build

Add config and metadata action types through all internal layers (types, translation, apply, conflict detection).

• UpdateConfig: Update table configuration (lance.* keys). Set/remove semantics.
• UpdateTableMetadata: Update arbitrary user key-value pairs. Set/remove semantics.
• SetDataFormat: Set the data storage format.
• SetFeatureFlags: Enable or clear reader/writer feature flags.
• ReserveFragmentIds: Increment max_fragment_id without adding fragments.

Operation translations:

• UpdateConfig → [UpdateConfig + UpdateTableMetadata + UpdateSchemaMetadata]
• ReserveFragments → [ReserveFragmentIds]

Each translation must round-trip losslessly.

Acceptance criteria

• All five action types defined and apply logic implemented
• Conflict detection for each action type
• Operation translations implemented with round-trip tests
• Existing update-config and reserve-fragments tests still pass

Blocked by

• Blocked by Tracer bullet: AddFragments action end-to-end (internal) #6449 (tracer bullet — need the framework)

User stories addressed

• User story 5: single code path for applying operations
• User story 9: old operations translated to actions
• User story 11: lossless round-trip