brew-graph: improve formatting.

This commit adds additional formatting options to the graph. Most noticeable is a top-to-bottom layout (rather than the previous left-to-right), and nicer fonts on everything.

More subtly, the ranking mechanism has been updated so that the "Safe to Remove" cluster is always at the highest rank (fixing a bug where non-leaf nodes could have been placed next to it,) and added better margins and padding. The rank separation was also decreased for a more compact graph.

Under the hood, the GraphViz output code was updated to support attributes with a list of sub-attributes (for example, 'graph [fontsize="11", fontname="Helvetica"]') and to not put quotes around HTML-like labels in clusters.

Closes #26651.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
libcoap: C implementation of CoAP (new formula)

Closes #24721.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>