Make interfaces more robust against untrusted input/misuse

[Dan-wanna-M]

Compiling schemas into kbnf engine is a very nontrivial process and unfortunately it is theoretically impossible to have a truly robust algorithm(in the sense of no accidental quadratic or even nonpolynomial complexity), but we can (and should) add some docs/warnings/assertions to ensure users' server wont accidentally use 77GB RAM(+VRAM) and killed by OS.

• DFA max memory cap
• Monitor potentially ambiguous CFG grammar?
• Warning on the exponential behavior of optional JSON fields support
• more comprehensive docs on this issue, maybe a separate dedicated page