feat(audio,android): add MobileVoiceAudioBackend + AndroidVoiceUnit (oboe-rs)

Add the cross-platform MobileVoiceAudioBackend trait, plus the
Android implementation AndroidVoiceUnit backed by oboe-rs 0.6.x.
AndroidVoiceUnit owns AAudio stream setup with VoiceCommunication
usage/preset, performance-mode LowLatency request, sharing-mode
Exclusive best-effort, hardware AEC/NS/AGC engagement via JNI, and
the diagnostics snapshot publish path used by SDD-116 evidence
collection.

Cargo.toml: adds oboe = "0.6" under the Android target.

Trace: SDD-111, SDD-112, SDD-113, SRS-210, SRS-211, SRS-212, SRS-213,
SRS-214.

Cargo.lock

@@ -393,6 +393,7 @@ dependencies = [
  "futures-util",
  "jni 0.21.1",
  "ndk-context",
+ "oboe",
  "rand 0.8.6",
  "reqwest",
  "sdl2",
@@ -2293,6 +2294,26 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "oboe"
+version = "0.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e8b61bebd49e5d43f5f8cc7ee2891c16e0f41ec7954d36bcb6c14c5e0de867fb"
+dependencies = [
+ "num-derive",
+ "num-traits",
+ "oboe-sys",
+]
+
+[[package]]
+name = "oboe-sys"
+version = "0.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c8bb09a4a2b1d668170cfe0a7d5bc103f8999fb316c98099b6a9939c9f2e79d"
+dependencies = [
+ "cc",
+]
+
 [[package]]
 name = "omnom"
 version = "3.0.0"