Make sol-dbg more resilient to missing contracts

[cd1m0]

In a previous commit we made sol-dbg a little resilient to missing contracts. But there is still a lot left to do:

1. Add a test where you have a contract A whose artifact is missing, but its referenced in the arguments, and getters of contract B.
2. Make sure that stack trace building for functions/getters that have B as an argument/return still work
3. Make sure that stack trace building/decoding kinda works for arguments that are structs/enums contained inside B. By kinda I mean that the whole frame is still decoded, with the relevant fields with missing information just marked as missing