Fix Olm receive on locally initiated sessions

[TroyHernandez]

Fix receiving Olm replies on sessions initiated by this client.

• Try both stored session directions before creating an inbound prekey session.
• Contain failed or replayed prekeys and malformed plaintext so sync can continue.
• Add optional existing-session handles to the standalone receive helper.
• Add 83 regression assertions using real Olm sessions, including persistence and replay cases.

Validation of the reviewed source, which is unchanged on this clean branch:

• mx.client: 405/405 assertions pass.
• chat.api: 1092/1092 assertions pass against the isolated mx.client build.
• Local package check: 0 errors, 0 warnings, 0 notes.

This PR changes only mx.client and raises no dependency floors. The 0.2.0.9
version bump is a separate DESCRIPTION/NEWS commit. The previously published
mx.api and mx.crypto development dependencies are available to CI through drat.

The existing limit of one session per direction per peer remains. A unified
per-peer session history is a follow-up. Live inbound decryption has not yet
been verified; deployment and that check remain separate.