Enhance kmir show with --statistics and --leaves (#707)

[Stevengre]

It is used to print better proof_status.md for solana-token, aiming to include all the information useful to fast investigate the result and update tests.md.

Example output with --statistics and --leaves:

STATISTICS
-----------
Total nodes: 10

Node roles (exclusive):
  failing : 2  ids: 10, 12
  split   : 1  ids: 6
  normal  : 7  ids: 3, 4, 5, 7, 8, 9, 11
  (root nodes omitted from totals: 1, 2)

Leaf paths from init:
  total leaves (non-root): 2
  reachable leaves       : 2
  total steps            : 2193

  leaf 10: steps 893, path 1 -> 3 -> 4 -> 5 -> 6 -> 8 -> 10
  leaf 12: steps 1300, path 1 -> 3 -> 4 -> 5 -> 6 -> 7 -> 9 -> 11 -> 12

LEAF <k> CELLS
---------------
Node 10:
  #traverseProjection ( toLocal ( 2 ) , AllocRef ( allocId ( 600719 ) , .ProjectionElems , noMetadata ) , projectionElemDeref  .ProjectionElems , .Contexts )
  ~> #readProjection ( false )
  ~> #freezer#discriminant(_,_)_RT-DATA_Evaluation_Evaluation_MaybeTy0_ ( ty ( 600110 ) ~> .K )
  ~> #freezer#setLocalValue(_,_)_RT-DATA_KItem_Place_Evaluation1_ ( place ( ... local: local ( 4 ) , projection: .ProjectionElems ) ~> .K )
  ~> #execStmts ( statement ( ... kind: statementKindAssign ( ... place: place ( ... local: local ( 0 ) , projection: .ProjectionElems ) , rvalue: rvalueBinaryOp ( binOpEq , operandCopy ( place ( ... local: local ( 3 ) , projection: .ProjectionElems ) ) , operandCopy ( place ( ... local: local ( 4 ) , projection: .ProjectionElems ) ) ) ) , span: span ( 621308 ) )  .Statements )
  ~> #execTerminator ( terminator ( ... kind: terminatorKindReturn , span: span ( 621307 ) ) )

Node 12:
  #execTerminator ( terminator ( ... kind: terminatorKindCall ( ... func: operandConstant ( constOperand ( ... span: span ( 603598 ) , userTy: noUserTypeAnnotationIndex , const: mirConst ( ... kind: constantKindZeroSized , ty: ty ( 600118 ) , id: mirConstId ( 39 ) ) ) ) , args: operandConstant ( constOperand ( ... span: span ( 603599 ) , userTy: noUserTypeAnnotationIndex , const: mirConst ( ... kind: constantKindAllocated ( allocation ( ... bytes: b"\x00\x00\x00\x00\x00\x00\x00\x00+\x00\x00\x00\x00\x00\x00\x00" , provenance: provenanceMap ( ... ptrs: provenanceMapEntry ( ... offset: 0 , allocId: allocId ( 600074 ) )  .ProvenanceMapEntries ) , align: align ( 8 ) , mutability: mutabilityMut ) ) , ty: ty ( 600073 ) , id: mirConstId ( 474 ) ) ) )  operandMove ( place ( ... local: local ( 5 ) , projection: .ProjectionElems ) )  .Operands , destination: place ( ... local: local ( 4 ) , projection: .ProjectionElems ) , target: noBasicBlockIdx , unwind: unwindActionCleanup ( basicBlockIdx ( 4 ) ) ) , span: span ( 603600 ) ) ) ~> .K

(cherry picked from commit 4a6892b)

[jberthold]

LGTM