CairoVM requirements

[enitrat]

Tracking our modification requirements from the CairoVM:

1. DictTrackers dictionaries:
   a. They only accept MaybeRelocatable as keys. As our keys don't necessarily fit in felts (hashdicts), we want to accept compound types as dictionary keys. action taken: a enum DictKey {Simple(MaybeRelocatable, Compound(Vec<MaybeRelocatable>)} as key type.
   b. dict.get, when used on a default dict, inserts that key in the dict. We don't want this happening: getting a default value should not create an entry in the tracker, but should simply log this in cairo.