oras push/attach should not allow colon in media type only on Windows

[qweeah]

Using oras 0.16.0, I can use below command to upload a layer with colon in the media type on Windows:

oras push localhost:5000/test:path .\KEYS:test:test:test

See layers.mediatype below, this command will generate a layer with test:test:test as an invalid media type

> oras manifest fetch localhost:5000/test:path --pretty
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.manifest.v1+json",
  "config": {
    "mediaType": "application/vnd.unknown.config.v1+json",
    "digest": "sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a",
    "size": 2
  },
  "layers": [
    {
      "mediaType": "test:test:test",
      "digest": "sha256:b79b04d85ebb8b289bde13387a5c6f3d98448d5a51937e6f94239303ffc2add8",
      "size": 15020,
      "annotations": {
        "org.opencontainers.image.title": "KEYS"
      }
    }
  ]
}

According to rfc2045 , colon is a special character and should not be in the media type. So the push command should show an error same to linux/darwin build:

> oras push localhost:5000/test:path .\KEYS:test:test:test
Error: failed to stat .KEYS:test:test: stat .KEYS:test:test: no such file or directory