Add/update the quantized ONNX model files and README.md for Transformers.js v3

## Applied Quantizations

### ✅ Based on `model.onnx` *with* slimming

↳ ❌ `int8`: `model_int8.onnx` (added but JS-based E2E test failed)
```
/home/ubuntu/src/tjsmigration/node_modules/.pnpm/[email protected]/node_modules/onnxruntime-node/dist/backend.js:25
__classPrivateFieldGet(this, _OnnxruntimeSessionHandler_inferenceSession, "f").loadModel(pathOrBuffer, options);
^

Error: Could not find an implementation for ConvInteger(10) node with name '/wav2vec2/feature_extractor/conv_layers.0/conv/Conv_quant'
at new OnnxruntimeSessionHandler (/home/ubuntu/src/tjsmigration/node_modules/.pnpm/[email protected]/node_modules/onnxruntime-node/dist/backend.js:25:92)
at Immediate.<anonymous> (/home/ubuntu/src/tjsmigration/node_modules/.pnpm/[email protected]/node_modules/onnxruntime-node/dist/backend.js:67:29)
at process.processImmediate (node:internal/timers:485:21)

Node.js v22.16.0
```
↳ ✅ `uint8`: `model_uint8.onnx` (added)
↳ ✅ `q4`: `model_q4.onnx` (added)
↳ ✅ `q4f16`: `model_q4f16.onnx` (added)
↳ ✅ `bnb4`: `model_bnb4.onnx` (added)

onnx/model_bnb4.onnx

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+size 222752457

onnx/model_q4.onnx

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+oid sha256:1e5aefb65ab9d4c54d7c081f85e08c5e10d8aab70e4d1a7aa9885ee74e48b495
+size 241674786

onnx/model_q4f16.onnx

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+oid sha256:61836c1429ae1cc2d51bbf9a11273eec604effa78c3ee3ff6fcc40921251a4eb
+size 196903041

onnx/model_uint8.onnx

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+oid sha256:4a2ee58baed7b791cb3481bf275745470e3c3fab2b5ebcc8619b718727d641b6
+size 317643153