Release v0.3.4

- Added VpxEncoderConfig.Builder: fluent builder API accessible via VpxEncoderConfig.builder(width, height)
- Nine new encoder config fields with full libvpx FFI wiring: rateControlMode (VBR/CBR/CQ/Q), maxKeyframeDistance, keyframeMode (AUTO/DISABLED), profile, usage, errorResilient, lagInFrames, maxQuantizer, minQuantizer
- Removed three short convenience constructors from VpxEncoderConfig in favour of the builder
- New VpxEncoderConfigBuilderTest suite covering defaults, round-trip, CBR encode, keyframe interval, error-resilient, and quantiser scenarios