Output in Jupyter notebooks for `rstac` classes

[OldLipe]

When using rstac in Jupyter notebooks, objects are printed using the default text representation. Providing an HTML output would improve readability and usability in notebook environments.

Proposed Change
Add HTML representations for rstac classes using S3 methods based on the repr package:

repr_html.class

Implement repr_html() methods for relevant rstac classes so they render nicely in Jupyter.

Expected Behavior

• In Jupyter notebooks, rstac objects display a formatted HTML representation.
• In non-notebook environments, behavior remains unchanged.

Acceptance Criteria

• repr_html() methods implemented for rstac classes.
• Output renders correctly in Jupyter notebooks.
• No change to existing console output.
• Tests added where applicable.