feat: add Pebbe v2 support

[tzdybal]

This PR introduces support for Pebble v2. As v1 and v2 are not compatible (data migration is required) new DB backend was introduced.

On the API level, v1 and v2 are very similar. To avoid code duplication, adapter pattern was used to hide v1 and v2 details.

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PR checklist

• Tests written/updated
• Changelog entry added in .changelog (we use unclog to manage our changelog)

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Note

Adds a new pebbledb2 backend (Pebble v2) and refactors PebbleDB to use an adapter that supports both Pebble v1 and v2, with tests and dependency updates.

• Storage Backends:
  • Add new backend Pebble2DBBackend (pebbledb2) and register creator in pebble.go/db.go.
• Implementation:
  • Refactor PebbleDB to wrap a pebbleDB interface; introduce adapters pebbleV1Adapter and pebbleV2Adapter plus batch/iter shim types.
  • Update Get/Set/Delete/batch commit paths to route through adapter and unify sync/no-sync options.
  • Iterator construction now uses unified pebbleIterOptions/pebbleIter.
  • DB() now returns underlying instance as any.
• Tests/Benchmarks:
  • Add TestPebble2DBBackend and BenchmarkPebble2DBRandomReadsWrites in pebble_test.go.
• Dependencies:
  • Bump github.com/cockroachdb/pebble to v1.1.5; add github.com/cockroachdb/pebble/v2 v2.1.1 and related indirect deps; update go.sum accordingly.

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[tzdybal]

Closing this as we're gonna work with our fork.