fix: nil-safe handle params and remove redundant int32() casts

Two systemic generated-code fixes:

1. Nil-safe handle access: generated methods now use .cptr() instead of
   .ptr for pointer handle params. The cptr() method returns nil when the
   receiver is nil, preventing SIGSEGV when passing nil optional params
   (e.g. nil surface/crypto in AMediaCodec_configure).

2. Generic result(): changed from result(int32) to result[T ~int32|~uint32]
   so capi return types are accepted directly without redundant int32() cast.

Also fixes media codec-lifecycle and decoder-setup examples to skip
Configure/Start when running outside an Activity context (C-level crash).

Author: xaionaro@dx.center