Added support for specifying multiple media types for a single codec

[abdelfetah18]

/claim #3284

// Before – this doesn't work correctly:
val mediaTypeJsonOrTextEndpoint = Endpoint(RoutePattern.POST / "api" / "mediaTypeJsonOrText")
  .outCodec(HttpCodec.content[Greeting](MediaType.text.plain))
  .outCodec(HttpCodec.content[Greeting](MediaType.application.json))

This approach fails because both codecs are defined for the same type (Greeting). The fallback mechanism isn't smart enough to distinguish based on media type and will always select the first codec, even if the client expects a different content type.

My Solution Is:

// Added support for multiple media types:
val mediaTypeJsonOrTextEndpoint = Endpoint(RoutePattern.POST / "api" / "mediaTypeJsonOrText")
  .outCodec(HttpCodec.content[Greeting](List(MediaType.text.plain, MediaType.application.json)))

To resolve this, I added support for specifying multiple media types for a single codec. Now the codec can respond with either plain text or JSON, depending on the Accept header, without relying on fallback behavior.

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