Py-trees

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* [blackboard] bugfix protection against activity stream not activitated for views, `140 <https://github.com/splintered-reality/py_trees_ros/pull/140>`_
* [trees] bugfix toggle for activity client on reconfigure, `139 <https://github.com/splintered-reality/py_trees_ros/pull/139>`_

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* [infra] add a marker file to assist with ros2cli discovery `138 <https://github.com/splintered-reality/py_trees_ros/pull/138>`_

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* [trees] on-demand snapshot stream services, similar to blackboard streams, `135 <https://github.com/splintered-reality/py_trees_ros/pull/135>`_, `#136 <https://github.com/splintered-reality/py_trees_ros/pull/136>`_

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* [trees] periodically publish snapshots, `131 <https://github.com/splintered-reality/py_trees_ros/pull/131>`_,
* [trees] permit setup visitors, provide a default with timings, `129 <https://github.com/splintered-reality/py_trees_ros/pull/129>`_
* [trees] bugfix non-infinite timeout arg getting ignored, `129 <https://github.com/splintered-reality/py_trees_ros/pull/129>`_
* [trees] snapshot now publishing tree changed flag and key access info, `128 <https://github.com/splintered-reality/py_trees_ros/pull/128>`_
* [utilities] deprecate myargv for rclpy.utilities.remove_ros_args, `130 <https://github.com/splintered-reality/py_trees_ros/pull/130>`_

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* [blackboards] updated pretty printing to differentiate namespace vs attribute access, `123 <https://github.com/splintered-reality/py_trees_ros/pull/123>`_
* [blackboards] api updates for namespaced clients, `122 <https://github.com/splintered-reality/py_trees_ros/pull/122>`_,
* [tests] migrated tests from unittest to pytest
* [transforms] behaviours for writing to and broadcasting from the blackboard, `121 <https://github.com/splintered-reality/py_trees_ros/pull/121>`_
* [transforms] add missing mocks and update to latest blackboard api, `125 <https://github.com/splintered-reality/py_trees_ros/pull/125>`_

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* [blackboard] client ``Blackboard.unregister_key()`` method