[Feature Request]: mark database as read-only to allow parallel concurrent reads

### Describe the problem

The documentation says that when using in memory instance, it will lock when trying to read data from the same index concurrently.
If I can "lock"/mark that database that its intended use is read only, is there a way to enable concurrent reading?

### Describe the proposed solution

when opening a database, mark that its read-only.
This may allow to have concurrent ready.

This works well when the database files are "frozen" and will not be concurrently updated while reading from the database.

### Alternatives considered

_No response_

### Importance

nice to have

### Additional Information

_No response_

No implementation files or tests are named. Start by reading the documentation about concurrent reads from in-memory databases, then trace how a database is opened and how read locking is handled. Done would require a defined read-only opening option, verified concurrent reads for frozen database files, and corresponding documentation or tests.

Written by the indexing model from the issue text.