Support access for specific inflight instants of MDT

### Task Description

**What needs to be done:**
- add access support of inflight instants for MDT
- these instants needs to be explicitly declared on the access API
- we can add a new API for RLI first to reduce the impact to existing code path
- add tests

**Why this task is needed:**

explained in https://github.com/apache/hudi/pull/17610#discussion_r2629548903

### Task Type

Code improvement/refactoring

### Related Issues

**Parent feature issue:** (if applicable )
#17647

Start by reading the access API and the RLI and MDT references in the issue, then review the linked discussion and parent issue #17647 for the required semantics. Add explicit support for selected inflight MDT instants through the access API, introduce the RLI API if needed to limit existing code-path impact, and add tests demonstrating the behavior.

Written by the indexing model from the issue text.