Cleanup Datomic facade so system fiddles can d/q without hardcoding a Datomic product line

[dustingetz]

https://github.com/hyperfiddle/hyperfiddle/blob/3dcd1dd786ec3a6dd0b487c0ea5744e53e96070e/src/hyperfiddle/foundation.cljc#L139

Userland fiddles e.g. hello-world are happy to hardcode the Datomic dep, but hf provided fiddles must be agnostic. The current Datomic facade sucks for this, needs untangling.

[dustingetz]

Due to forbidden datomic imports in the submodule, clj -m compile-cljs must be clj -A:free -m compile-cljs so the cljc files that assume datomic.api are well-formed or this fails. (The cljs compiler pulls a bunch of JVM files in to load the hf-def macro stuff for #1094 def hacks)