refactor: substitute by invoking the field's own engine encoder (slot 0)

Replaces hand-rolled per-type bit-writes with one generic call: resolve the
per-field encoder = *(*(fieldInfo+0x38)) (slot 0), build paramsPtr from
fieldInfo+0x40/0xc9, write the fake into a scratch in the engine's native layout
(int64/uint64/byte/double), call enc(dst, fieldInfo, paramsPtr, scratch, 0).
Correct bit-format by construction for int/uint/int64/uint64/bool/float32/fixed32/
fixed64. Deleted WriteUBitLong + the VarintWriter gamedata entry/resolution
(IntEncoderDetour Phase-1 doesn't use it). Quantized/coord/normal/string/array
stay passthrough (value layout not synthesizable). Fault->restore cursor, never
double-call original. Build 0/0.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>