New visitor SidecarVisitor and Sidecar action struct

[sebastiantia]

Please describe why this is necessary.

These changes are part of V2 checkpoint read support.
For a scan, we need to build the list of add and remove actions required to make up the table’s state. These changes are required to read the necessary actions in sidecar files referenced by V2 checkpoints.

Describe the functionality you are proposing.

• New SidecarVisitor which visits checkpoint batches to collect all sidecar file paths found in sidecar actions
• New Sidecar struct to model the new sidecar actions

Additional context

No response