feat: expose moq-pub as library with generic input

[Frando]

This PR has two changes, which allow to reuse the code in moq-pub from other libraries or apps:

• adds a lib.rs to moq-pub to expose the media module
• lets the Media struct accept an input: impl AsyncRead argument instead of being hardcoded to stdin

[kixelated]

although there be a LINT FAILURE.

[Frando]

The failure seems unrelated to me?

error: unused import: `string::*`
Error:   --> moq-transport/src/coding/mod.rs:10:9
   |
10 | pub use string::*;
   |         ^^^^^^^^^
   |
   = note: `-D unused-imports` implied by `-D warnings`

[kixelated]

Sorry for the delay!