Slow call to `olmMachine.getRoomSettings()`

A bit of context first: we are migrating from the legacy crypto stack to rust crypto stack. In EW, we need to know if the room is encrypted to display it. This assertion is a part of the critical path of EW.

To know if the room is encrypted, we look at the room settings thanks to [`olmMachine.getRoomSettings()`](https://github.com/matrix-org/matrix-js-sdk/blob/develop/src/rust-crypto/rust-crypto.ts#L387).

We have spot a performance issue when trying to get this value from less than 1sec to multiple secs to respond.

Start with the referenced olmMachine.getRoomSettings() entry point in src/rust-crypto/rust-crypto.ts and profile the call when checking whether a room is encrypted. Trace the slow path into the Rust crypto implementation, then verify that the lookup consistently avoids multi-second responses in the critical path.

Written by the indexing model from the issue text.