Turn the price calculation into a jinja template

[gkaracha]

Other changes

• To avoid some cyclic dependencies I moved some utility functions from checker.ml to checkerTypes.ml, since they pertain to the external_contracts type.
• Renamed kit_in_tez to kit_in_tok in places where it was misspelled; there's no tez anywhere in Checker at the moment, tok captures the collateral type.
• Added src/price.mli
• BugFix: replaced tez_scaling_factor_int by tok_scaling_factor_int and removed tez_scaling_factor_int altogether; these places would erroneously use a scaling factor of 1_000_000 even if the FA2 token used as collateral has a different scaling factor. While at it, I also removed fraction_to_tez_floor and tez_scaling_factor_nat that were no longer needed either.
• Also added scripts/builder/checker_builder/templates/fa2Price.ml.jinja already and checked that we can use it successfully to calculate the price (e2e tests should pass, I mean).

[github-actions[bot]]

Gas costs	6905d6e45a379c13a6d6b02bc176239feabb333f	caa82c80f357b36e075a5bd8a665a21b07280ada	Diff
checker%touch	42381	42391	10

Entrypoint sizes	6905d6e45a379c13a6d6b02bc176239feabb333f	caa82c80f357b36e075a5bd8a665a21b07280ada	Diff
touch	56749	56753	4

Test coverage	6905d6e45a379c13a6d6b02bc176239feabb333f	caa82c80f357b36e075a5bd8a665a21b07280ada	Diff
checkerTypes.ml	100	77.78	-22.22
price.ml	83.33	76.92	-6.409999999999997
checker.ml	93.87	94.93	1.0600000000000023

[github-actions[bot]]

Gas costs	560d987ee595fc2edea476a5c28796f719a08a94	bad559751a6e802286a4cc4f20d53e5dcd8f3b4a	Diff
checker%deactivate_burrow	23258	23259	1
checker%update_operators	5590	5591	1
checker%touch	42381	42380	-1
checker%add_liquidity	12466	12467	1

Entrypoint sizes	560d987ee595fc2edea476a5c28796f719a08a94	bad559751a6e802286a4cc4f20d53e5dcd8f3b4a	Diff
liquidation_auction_place_bid	2173	2141	-32
mark_for_liquidation	16965	16949	-16

Test coverage	560d987ee595fc2edea476a5c28796f719a08a94	bad559751a6e802286a4cc4f20d53e5dcd8f3b4a	Diff
checkerTypes.ml	100	77.78	-22.22
price.ml	83.33	76.92	-6.409999999999997
checker.ml	93.87	94.93	1.0600000000000023
common.ml	97.89	97.59	-0.29999999999999716
TOTAL	92.49	92.45	-0.03999999999999204

[gkaracha]

Thanks!