fix: toSnakeCase treating each uppercase letter as a word boundary

The function was designed for PascalCase (StreamBuilder → stream_builder)
but received ALL_CAPS input (AUDIO, IMAGE_FORMATS) from autoGoTypeName,
producing absurd filenames like a_u_d_i_o.go and i_m_a_g_e__f_o_r_m_a_t_s.go.

Fix: only insert underscore on lowercase/digit → uppercase transitions.
Regenerated all idiomatic packages (195 files renamed).

Also replace magic constants in examples with exported package constants:
- looper: use ALOOPER_POLL_WAKE etc. instead of redeclared int32(-1)
- camera/display: use media.AIMAGE_FORMAT_PRIVATE/YUV_420_888 instead of
  hex literals (old comment was wrong: 0x22 is PRIVATE, not YUV_420_888)

Author: xaionaro@dx.center