Java SDK: add lifecycle processing_interval setting

[mother-6000]

Parent: reductstore/reductstore#1577
Core implementation: reductstore/reductstore#1549
Original feature request: reductstore/reductstore#1463
Docs PR: reductstore/website#364

ReductStore Core now supports an optional lifecycle processing_interval setting in the HTTP API and RS_LIFECYCLE_<ID>_PROCESSING_INTERVAL provisioning. The field bounds how much data time a single lifecycle run processes.

Behavior to expose:

• API field: processing_interval
• Provisioning env var: RS_LIFECYCLE_<ID>_PROCESSING_INTERVAL
• Example values: 6h, 12h, 1d
• Default: unset / None, preserving the existing 24 * interval data window behavior
• Validation: server requires a positive duration
• Applies to delete and compress lifecycle policies
• When system events are disabled, it still clamps the full-range processing window

Scope:

• Add processing_interval to the Java SDK lifecycle policy settings model/types.
• Ensure lifecycle create/update/get/list flows serialize and deserialize the field.
• Update examples/tests/changelog as appropriate.

Acceptance criteria:

• A user can pass processing_interval when creating or updating a lifecycle policy.
• Returned lifecycle policy settings expose processing_interval when present.
• Omitting processing_interval remains backward compatible and preserves existing behavior.
• Tests cover serialization/deserialization and user-facing create/update paths where practical.