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/onnxruntime-node@1.21.0/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 '/backbone/embeddings/patch_embeddings/projection/Conv_quant'
at new OnnxruntimeSessionHandler (/home/ubuntu/src/tjsmigration/node_modules/.pnpm/onnxruntime-node@1.21.0/node_modules/onnxruntime-node/dist/backend.js:25:92)
at Immediate.<anonymous> (/home/ubuntu/src/tjsmigration/node_modules/.pnpm/onnxruntime-node@1.21.0/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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+version https://git-lfs.github.com/spec/v1
+oid sha256:2392aba77bd34e7183ae58d3395b9d5dbfaf9eba8da7fc1f71afdcb59b211f65
+size 26236495

onnx/model_q4.onnx

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+oid sha256:dfa44107860895b9aa7ac074f55b74427772302a86812f513e8820ffab192bec
+size 27563143

onnx/model_q4f16.onnx

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+oid sha256:dd2f330c2cf62fd056a0cbf9032f860d62f31f3074826f0d23de3ffa7d3516e4
+size 20336189

onnx/model_uint8.onnx

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+oid sha256:4c307cbb44117199ec1672d860d845bce111301a0dcbcf05f334f88599480cfd
+size 27256285