Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked	Calltree index	Parent function	Callsite	Largest blocked function
4	0	EP	call site: 00000	.open

Fuzzer calltree


         ...fuzz_source.TestOneInput

[function] [call site] 00000


           <builtin>.open

[function] [call site] 00001


           f.write

[function] [call site] 00002


           executing.Source.for_filename

[function] [call site] 00003


           <builtin>.list

[function] [call site] 00004