Improved show printing for leaves

[dkcumming]

Short Version

This PR:

• Threads Spans through to #setUpCalleeData instead of being ignored from the Terminator
• Modifies the python utility code that prints leaves for kmir show --leaves to print function, call site, and error messages when possible for panic and assert_failed
• Adds the ability to truncate a path for testing so CI is deterministic

Long Version

In the event that a panic or assert_failed is reached in a proof, a stuck leaf node will be present in the KCFG that calls ** UNKNOWN FUNCTION **. It is not clear exactly which function is being called, where this is being called from, or what the error message is (if there is one) as all the information is represented as interned data (DefId, Span, AllocId).

The print out of the failing nodes is improved for kmir show --leaves from:

Node 3:
  #setUpCalleeData ( monoItemFn ( ... name: symbol ( "** UNKNOWN FUNCTION **" ) , id: defId ( 38 ) , body: noBody ) , operandConstant ( constOperand ( ... span: span ( 32 ) , userTy: noUserTypeAnnotationIndex , const: mirConst ( ... kind: constantKindAllocated ( allocation ( ... bytes: b"\x00\x00\x00\x00\x00\x00\x00\x00\x17\x00\x00\x00\x00\x00\x00\x00" , provenance: provenanceMap ( ... ptrs: provenanceMapEntry ( ... offset: 0 , allocId: allocId ( 1 ) )  .ProvenanceMapEntries ) , align: align ( 8 ) , mutability: mutabilityMut ) ) , ty: ty ( 39 ) , id: mirConstId ( 25 ) ) ) )  .Operands) ~> .K

to:

Node 3:
  #setUpCalleeData ( monoItemFn ( ... name: symbol ( "** UNKNOWN FUNCTION **" ) , id: defId ( 38 ) , body: noBody ) , operandConstant ( constOperand ( ... span: span ( 32 ) , userTy: noUserTypeAnnotationIndex , const: mirConst ( ... kind: constantKindAllocated ( allocation ( ... bytes: b"\x00\x00\x00\x00\x00\x00\x00\x00\x17\x00\x00\x00\x00\x00\x00\x00" , provenance: provenanceMap ( ... ptrs: provenanceMapEntry ( ... offset: 0 , allocId: allocId ( 1 ) )  .ProvenanceMapEntries ) , align: align ( 8 ) , mutability: mutabilityMut ) ) , ty: ty ( 39 ) , id: mirConstId ( 25 ) ) ) )  .Operands , span ( 117 ) ) ~> .K
  >> function: core::panicking::panic::h941160ead03e2d54
  >> call span: /home/daniel/Applications/mir-semantics/kmir/src/tests/integration/data/prove-rs/symbolic-args-fail.rs:53:5
  >> message: 'assertion failed: false'

This is achieved by taking advantage of the deterministic location of the interned values, retrieving those values, and then consulting the .smir.json to get the un-interned data associated with those interned values.