Avoid runtime re-reads if possible

This pull request refactors the initialization and property access patterns in the PointCloudsComponent class to improve efficiency and code clarity. The main change is the introduction of an explicit __init__ method that caches frequently accessed attributes, reducing repeated reads from the underlying data group.

Refactoring and performance improvements:

• Added an __init__ method to the class to cache pc_timestamps_us, coordinate_unit, and attribute_schemas as instance variables, reducing repeated access to the underlying zarr.Group and improving performance.
• Updated the coordinate_unit, pcs_count, pc_timestamps_us, and attribute_names properties to return values from the cached instance variables instead of reading from the group each time.
• Modified the get_attribute_schema method to use the cached _attribute_schemas dictionary, ensuring consistent and efficient schema access.