Pass uint32_t (or uint64_t when USE_API_VARINT64 is defined) directly
to decode_varint() instead of the ProtoVarIntResult struct. This
eliminates accessor method overhead in each of the 51 overrides,
replacing value.as_uint32() with direct value usage, value.as_bool()
with value != 0, etc. No vtable growth - single virtual method with
conditionally-typed parameter.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>