[difftest] Add offline difftest and refactor libspike interfaces #2592

Job	Run time
Test elaborate	2m 35s
Generate test plan	6s
Build Emulators (blastoise)	2m 15s
Build trace emulator (blastoise)	2m 16s
Build Emulators (machamp)	2m 16s
Build trace emulator (machamp)	2m 16s
Build Emulators (sandslash)	2m 16s
Build trace emulator (sandslash)	2m 16s
Request physical design report	1s
Prepare for running testcases	1s
Run testcases	1s
Clean test reports [ON CANCELLED]	4s
Report CI result	1s
	16m 24s

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