Add lazy, cheaply guarded proxy-conversions.

[luukvanderduim]

This introduces lazy and cheaply guarded proxy-conversions.

It adds ObjectProxies which extends `AccessibleProxy

We have an easy conversion from ObjectRef to AccessibleProxy

AccessibleProxy::get_interfaces gives insight into which interfaces are unokenebted by the object.

ObjectProxies::proxies returns Proxies, a struct that can contain zero or more proxies to the objects supported interfaces.

The proxies are created only when needed and the check against the InterfaceSet is a cheap bitwise operation.

// Provided by `ObjectRefExt`
let accessible = obj.as_accessible_proxy();

// Provided by `ObjectProxies` extending `AccessibleProxy`
// Aqcuiring `Proxies` needs to be async to get supported interfaces.
let proxies = accessible.proxies().await?;

{
    let action = proxies.action()?; // init and return &mut `ActionProxy`
    let text = proxies.text()?;
}

let action = proxies.action()?; // already initialized! Return   

[codecov]

Codecov Report

Attention: Patch coverage is 2.04082% with 144 lines in your changes missing coverage. Please review.

Project coverage is 82.14%. Comparing base (a92b8f6) to head (4c59c24).
Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
atspi-proxies/src/proxy_ext.rs	0.00%	141 Missing ⚠️
atspi-common/src/error.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #202      +/-   ##
==========================================
- Coverage   83.87%   82.14%   -1.73%     
==========================================
  Files          43       44       +1     
  Lines        3231     3299      +68     
==========================================
  Hits         2710     2710              
- Misses        521      589      +68     

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[TTWNO]

Rebased

[TTWNO]

I'd appreciate something like ProxyExt or something like that. Thoughts?

[luukvanderduim]

Isn't naming supposed to be the hardest thing in software engineering?
ProxyExt sounds just fine.

[TTWNO]

Implementation is good.

[TTWNO]

@luukvanderduim are you okay with merging this?