Save trace of the found bug correctly

[Raz0r]

This pull request fixes a bug when ityfuzz finds a solution but the call trace for the corresponding input is not copied in work_dir/traces directory as "bug_{}.json".

The following block in cov_stage.rs never returns any results:

https://github.com/fuzzland/ityfuzz/blob/master/src/evm/cov_stage.rs#L171-L177

This happens because meta.corpus_idx_to_bug is checked before the bug info is inserted into it in https://github.com/fuzzland/ityfuzz/blob/master/src/oracle.rs#L145
Even if running with --run-forever I cannot find bug_{}.json in the traces directory.

I moved this logic into src/fuzzer.rs after an oracle reports a solution so that the trace with current input id is copied to a new file.

[fuzzland-bot]

Found: 19

Project Name	Vulnerability Found	Time Taken	Log
BIGFI_exp.txt	✅ Price Manipulation	0h-1m-55s	Log File
Shadowfi_exp.txt	❌	-1	Log File
SEAMAN_exp.txt	✅ Fund Loss	0h-1m-14s	Log File
BEGO_exp.txt	✅ Fund Loss	0h-0m-34s	Log File
cftoken_exp.txt	✅ Price Manipulation	0h-0m-48s	Log File
Carrot_exp.txt	✅ Arbitrary Call	0h-0m-46s	Log File
MBC_ZZSH_exp.txt	❌	-1	Log File
AUR_exp.txt	❌	-1	Log File
SellToken_exp.txt	✅ Fund Loss	0h-1m-23s	Log File
ROI_exp.txt	✅ Fund Loss	0h-0m-26s	Log File
GPT_exp.txt	❌	-1	Log File
OLIFE_exp.txt	❌	-1	Log File
THB_exp.txt	❌	-1	Log File
VerilogCTF.txt	❌‼️ Crashed	-1	Log File
CS_exp.txt	✅ Price Manipulation	0h-1m-14s	Log File
MintoFinance_exp.txt	✅ Fund Loss	0h-0m-42s	Log File
Novo_exp.txt	✅ Price Manipulation	0h-2m-4s	Log File
SELLC03_exp.txt	✅ Fund Loss	0h-2m-44s	Log File
Yyds_exp.txt	✅ Fund Loss	0h-2m-11s	Log File
DYNA_exp.txt	❌	-1	Log File
EAC_exp.txt	✅ Fund Loss	0h-2m-50s	Log File
Annex_exp.txt	❌	-1	Log File
PLTD_exp.txt	✅ Price Manipulation	0h-4m-5s	Log File
ApeDAO_exp.txt	✅ Price Manipulation	0h-0m-52s	Log File
GSS_exp.txt	✅ Fund Loss	0h-3m-3s	Log File
Axioma_exp.txt	✅ Fund Loss	0h-1m-30s	Log File
RFB_exp.txt	✅ Fund Loss	0h-2m-30s	Log File
HEALTH_exp.txt	✅ Price Manipulation	0h-0m-15s	Log File