Clean up typescript types related to rust crypto (#4706)

* Simplify bootstrapSecretStorage logic

might as well just export the keys immediately, rather than having multiple
tests.

* Clean up typescript types related to rust crypto

A forthcoming release of matrix-rust-sdk-crypto-wasm tightens up a number of
typescript types. In preparation, we need to get our house in order too.

spec/unit/rust-crypto/OutgoingRequestProcessor.spec.ts

@@ -56,6 +56,7 @@ describe("OutgoingRequestProcessor", () => {
         return new Promise((resolve, _reject) => {
             olmMachine.markRequestAsSent.mockImplementationOnce(async () => {
                 resolve(undefined);
+                return true;
             });
         });
     }