Adds support for the Property resource type in bindings.json, enabling
users to read connector-defined property values (e.g. SharePoint folder
IDs) without writing custom helpers.

- Extend BindingResourceValue with optional description/propertyName fields
- Add "property" to GenericResourceOverwrite (replaces a separate class)
- Add BindingsService with get_property() that reads from bindings.json
  and respects runtime resource overwrites via the existing ContextVar
- Expose sdk.bindings as a cached_property on the UiPath class
- Update bindings.spec.md to document Property as the 7th resource type
- Add unit tests covering file reads, suffix key matching, runtime
  overwrites (including Studio-loaded and real runtime payload formats),
  and error cases

ResourceOverwriteParser.parse now normalises the Property key prefix
to lowercase ("Property" -> "property") and accepts the real runtime
flat-dict format in addition to the explicit {"values": {...}} form.
Both changes are additive — existing valid inputs are unaffected.