fix: NUL-terminate ADB OPEN destinations

[atty303]

Problem

On an Android 7 device, a direct USB push consistently failed while opening the sync: service:

ADB request failed - Open session failed: got CLSE in response instead of OKAY

The same push succeeded through an ADB server connection.

adb_client sent the OPEN destination without a trailing NUL. AOSP adb NUL-terminates this payload and notes that adbd expects a null-terminated string:

https://android.googlesource.com/platform/system/core/+/dc29476d7e029e6c477c133b71ca55d52ee95744/adb/sockets.cpp#480

Verification

• Reproduced the direct USB push failure on an Android 7 device before this patch
• Confirmed the same direct USB push succeeds on that device after this patch
• cargo test -p adb_client

Note

The investigation and implementation were performed with OpenAI Codex.

[cocool97]

Thanks for the fix ! :)