DAL/Node: make explicit the time to connect to new topics

What and why

The commits are:

• Introduce variables for parameters in constants.ml (and use them). In this way it is easier to see which values will need updating when the parameters change.
• Update Constants.traps_cache_size to make it dependent on DAL parameters instead of hard-coding some value.
• Make explicit the time needed to connect to new topics, to be more resilient to changes in the block time. Closes #8087 (closed).
• Rename cache to not_yet_published_cache (not great, better suggestions welcome) to be more specific, as the DAL not maintains more caches, not just one.
• Remove reference to closed issue.