fix: resolve compilation errors in generated AIDL stubs

Fix five categories of bugs in the stub code generator:

1. Missing imports: always import context and parcel packages since the
   stub's OnTransaction method references them even for method-less
   interfaces.

2. Out parameter handling: pass zero-valued variables for AIDL `out`
   parameters to the implementation call instead of omitting them,
   which caused "not enough arguments" errors.

3. Duplicate switch cases: track used transaction codes and skip
   methods that resolve to an already-emitted code.

4. Builtin shadowing: add Go built-in function names (len, cap, make,
   etc.) to the reserved identifier set so AIDL parameters named after
   them get suffixed with underscore.

5. Import alias collision: rename the stub's parcel parameter from
   `data` to `_data` to avoid conflicts with import aliases like
   `data` for android.hardware.radio.data.

Additionally:
- Handle nullable non-cast stub params by taking address of read value
  to match the pointer-typed interface parameter.
- Detect Go type name collisions from nested AIDL types (e.g.,
  VolumeShaper.Configuration vs VolumeShaperConfiguration) and skip
  the empty forward-declared definition.
- Update package_query example to match new IsPackageAvailable
  signature (userId is now auto-filled from CallerIdentity).

Author: xaionaro@dx.center