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 0% with 143 lines in your changes missing coverage. Please review.

Project coverage is 83.46%. Comparing base (e8fa63c) to head (efbff96).
Report is 6 commits behind head on main.

Files	Patch %	Lines
atspi-proxies/src/related_proxies.rs	0.00%	141 Missing ⚠️
atspi-common/src/error.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #202      +/-   ##
==========================================
- Coverage   87.22%   83.46%   -3.77%     
==========================================
  Files          40       41       +1     
  Lines        3508     3665     +157     
==========================================
- Hits         3060     3059       -1     
- Misses        448      606     +158     

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