Add 'bus-tree' example

[luukvanderduim]

Addresses issue #173

• Adds the 'bus-tree' example

~~Also try out static_assertions::assert_cfg! to inform users of the appropriate features to use. This will make rust-analyzer noisy if you don't have these set in your editor.~~

• Add [[example]] section in Cargo.toml, which allows us to point out, using the required-features list which features a user needs.

This tries to add .vscode/settings.json to mitigate that but if this is deemed too opinionated, just remove it. removed, no longer needed.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.

Project coverage is 86.54%. Comparing base (6d5595c) to head (9a1e134).

Files	Patch %	Lines
atspi-proxies/src/accessible.rs	0.00%	14 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #188 +/- ## ========================================== - Coverage 86.69% 86.54% -0.16% ========================================== Files 39 39 Lines 3337 3344 +7 ========================================== + Hits 2893 2894 +1 - Misses 444 450 +6 ```

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[TTWNO]

@luukvanderduim is it possible, knowing what we know able Libreoffice Calc (2^31 children-cells), could you please add functionality for modelling "countable but almost infinite children"?

[luukvanderduim]

@luukvanderduim is it possible, knowing what we know able Libreoffice Calc (2^31 children-cells), could you please add functionality for modelling "countable but almost infinite children"?

Yeah.. it comes at the cost of adding a call per child to get the number of children.

A reasonable number:

• 65536 children (2^16) Children, which is max_descendants in the Object interface.

  A legal threshold:

• 12810241024 (Max Message size) / 48 (Size of an ObjectRef) = 2_708_821 children.

Or without the extra call. This will cover all stalling responses not just for (in practical terms) infinite children.

• A timeout (eg. 1 sec.)

[TTWNO]

65536 children (2^16) Children, which is max_descendants in the Object interface.

This seems good to me.

[luukvanderduim]

Last commit confirmed to make the example resilient against an 'infinite' number of children.