Panic on non-actionable failures

This is based on Michael's comments on aosp/2280849. For methods which
should never fail unless the VM is already dying, and for which
clients cannot take any meaningful action, panic instead of returning
false. Make sure we log the cause first.

Update client code to match. Update doc comments in the header file.

Also clarify that calling notify read more than once is harmless
(otherwise it would panic).

Incidentally, rename vs_payload_service.rs because it was confusing me
(we have a file of the same name in microdroid manager which actually
implements the service.)

Changes to AVmPayload_runVsockRpcServer will come later.

Bug: 243512108
Test: atest MicrodroidTests
Test: composd_cmd --test-compile
Change-Id: Ie6f6203ba54246cac669f4a68e8ab76f0a5792ae
diff --git a/vm_payload/src/lib.rs b/vm_payload/src/lib.rs
index be6cf93..5c3ee31 100644
--- a/vm_payload/src/lib.rs
+++ b/vm_payload/src/lib.rs
@@ -14,9 +14,9 @@
 
 //! Library for payload to communicate with the Microdroid Manager.
 
-mod vm_payload_service;
+mod api;
 
-pub use vm_payload_service::{
+pub use api::{
     AVmPayload_getDiceAttestationCdi, AVmPayload_getDiceAttestationChain,
     AVmPayload_getVmInstanceSecret, AVmPayload_notifyPayloadReady,
 };