nested runners on large rule numbers cannot compile

[chris-twiner]

on a feathered 400 top level rules to max 200 rules suite calls (so 400 rulesuites in Lits), janino cannot compile the generated code. This requires moving to nested contexts and separate compilation

[chris-twiner]

this impl passes the oss tests, not yet been tested on DBR, possibly should move to a var class param to allow both serialising and copy to work.

[chris-twiner]

per #129 tested on DBR 18.2 via 181 split compilation (compilation time from 30s to 15s and memory requirements from 12gb down to 2gb