[sample gen] `bytes` is un-supported encode

[v-jiaodi]

Issue from setting is-modular-library true for data plane: https://github.com/Azure/azure-rest-api-specs/tree/main/specification/loadtestservice/data-plane/loadtesting
generate code:

  const result = await client.uploadTestFile(
    "12345678-1234-1234-1234-123456789012",
    "sample.jmx",
    Buffer.from("application/octet-stream content", "bytes"),
    { fileType: "ADDITIONAL_ARTIFACTS" },
  );

modular ut as follow:

# Should generate samples for bytes parameters with correct encoding

Sample generation should handle bytes type parameters and use correct Buffer encoding.

## TypeSpec

```tsp
@doc("Upload a file as bytes")
op uploadFile(
  @doc("The file content as bytes")
  @bodyRoot
  fileContent: bytes
): { @body body: {} };

Example

{
  "title": "uploadFile",
  "operationId": "uploadFile",
  "parameters": {
    "fileContent": "application/octet-stream content"
  },
  "responses": {
    "200": {}
  }
}