feat!: CopyDataSource from static sources

[gibbz00]

This PR changes CopyDataSource::Data from containing a Vec<u8> to a Cow<'static, [u8]>, and then provides additional From<{&'static u8,&'static str,String}> implementation for it.

The motivation for this breaking change is admittedly mostly aesthetic.

fn new(config: impl Into<CopyDataSource>) -> SomeContainer;

const CONFIG: &str = r#"
  name = "foo"
  enabled = true
"#;

// Before:
let container = SomeContainer::new(CONFIG.as_bytes().to_vec());
// After:
let container = SomeContainer::new(CONFIG);

The first change will break compilation for projects that construct CopyDataSource directly with CopyDataSource::Data(vec). Those using impl Into<CopyDataSource> are unaffected by this change. Hopefully, most users construct CopyDataSource with the latter alternative. testcontainers-modules does this exclusively.

Another alternative could be to extend the enum with a third variant:

pub enum CopyDataSource {
    File(PathBuf),
    Data(Vec<u8>),
    StaticData(&'static u8),
}

This is also a breaking change, but only for those performing pattern matching on CopyDataSource, to which I assume a lot fewer do.

Completely understandable if this PR gets rejected given the questionable gains from such a breaking change ✌️

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