feat: add CheckpointVisitor in new checkpoint mod (#738)

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## What changes are proposed in this pull request?
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### Key changes

resolves #737. 

This PR implements the `CheckpointVisitor` necessary for filtering a
stream of actions into a stream of actions to be included in a
checkpoint file. This leverages the `FileActionDeduplicator` [[link to
PR]](#769).

This PR introduces the `checkpoint` mod, and implements the visitor in
the new `checkpoint/log_replay` mod.

Comprehensive module documents are included in the new modules which
provide an overview of the incoming code additions, along with it's
goal.


### Checkpoint Content 

A **complete V1 checkpoint** encapsulates:
1. All FILE actions that make up the state of a version of a table:
    - Add actions (after action reconciliation)
- Unexpired remove actions ([remove
tombstones](https://github.com/delta-io/delta/blob/master/PROTOCOL.md#add-file-and-remove-file))
2. All NON-FILE actions that make up the state of a version of a table:
    - Protocol action
    - Metadata action
    - Txn actions

A **single-file V2 checkpoint** is simply a super-set of the actions
included in the V1 checkpoint schema, with the addition of the
`CheckpointMetadata` action (which must be generated on every write).
Since single-file v2 checkpoints will also leverage this visitor, we
have chosen to name it the general `CheckpointVisitor`
    
Note: 
- CDC, CommitInfo, Sidecar, and CheckpointMetadata actions are NOT part
of the **V1** checkpoint schema.
- Sidecar and CheckpointMetadata actions are part of the **V2**
checkpoint schema.

### The new `CheckpointVisitor`
This visitor selects the **FILE** actions for a V1 spec checkpoint via a
selection vector:
1. Processes add/remove actions with proper deduplication based on path
and deletion vector ID pairs
2. Optimization: Only tracks already seen file paths in **commit
files**, as actions in checkpoint files are the last batches to be
processed, and do not conflict with other actions in checkpoint files.
3. Applies tombstone expiration logic by filtering out remove actions
with deletion timestamps older than the minimum file retention timestamp

This visitor also selects the **NON-FILE** actions for a V1 spec
checkpoint via a selection vector:
1. Ensures exactly one protocol action is included (the newest one
encountered)
2. Ensures exactly one metadata action is included (the newest one
encountered)
3. Deduplicates transaction (txn) actions by app ID to include only the
newest action for each app ID

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## How was this change tested?
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`test_checkpoint_visitor` - Tests basic functionality with both file and
non-file actions, verifying correct counts and selection vector.

`test_checkpoint_visitor_boundary_cases_for_tombstone_expiration` -
Tests how tombstone expiration handles threshold boundary conditions.

`test_checkpoint_visitor_conflicting_file_actions_in_log_batch` -
Verifies duplicate path handling in log batches (keeping first, skipping
second).

`test_checkpoint_visitor_file_actions_in_checkpoint_batch` - Tests that
duplicate file actions are included in checkpoint batches.

`test_checkpoint_visitor_conflicts_with_deletion_vectors` - Tests file
deduplication with deletion vectors to ensure uniqueness.

`test_checkpoint_visitor_already_seen_non_file_actions` - Verifies that
pre-populated actions are skipped correctly.

`test_checkpoint_visitor_duplicate_non_file_actions` - Tests
deduplication of non-file actions (protocol, metadata, transactions).

Author: sebastiantia