Add deconstructing conversions for owned Elements

[jpschorr]

Allows deconstruction owned Elements and Bytes into their contained data.

See also previous enhancements to ergonomics of owned Elements
Cf. #858
Cf. #866

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[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 77.86%. Comparing base (75b0763) to head (ed56ad0).

Files with missing lines	Patch %	Lines
src/element/mod.rs	90.47%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #890   +/-   ##
=======================================
  Coverage   77.85%   77.86%           
=======================================
  Files         136      136           
  Lines       34703    34727   +24     
  Branches    34703    34727   +24     
=======================================
+ Hits        27017    27039   +22     
- Misses       5683     5685    +2     
  Partials     2003     2003           

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[popematt]

Overall, looks good. I could see some of these maybe being better served by a From implementation, such as into_value and into_bytes. What do you think?

[popematt]

What are your thoughts on into_bytes() vs impl From<Bytes> for Vec<u8>? It might be more ergonomic because then Bytes could be passed to a function that accepts Into<Vec<u8>> . On the other hand, if we think we might ever have a lazy Bytes, then maybe it's best to leave it the way it is. @zslayton what do you think?

[jpschorr]

impl From<Element> for Value conflicts with the already present Value to Element From implementation.

// Anything that can be turned into a `Value` can then be turned into an `Element`
// by associating it with an empty annotations sequence.
impl<T> From<T> for Element
where
    T: Into<Value>,
{
    fn from(value: T) -> Self {
        Element::new(Annotations::empty(), value.into())
    }
}

impl From<Element> for Value {
    fn from(element: Element) -> Self {
        element.value
    }
}

error[E0119]: conflicting implementations of trait `From<element::Element>` for type `element::Element`
   --> src/element/mod.rs:973:1
    |
973 | / impl<T> From<T> for Element
974 | | where
975 | |     T: Into<Value>,
    | |___________________^
    |
    = note: conflicting implementation in crate `core`:
            - impl<T> From<T> for T;

[jpschorr]

I have changed the into_bytes into a From<Bytes> for Vec<u8>, though I could change it back if desired (or have both). It was inspired by https://doc.rust-lang.org/std/string/struct.String.html#method.into_bytes