[Compiler] Optimize compilation time

[JonathanMace]

With Blueprintv2, compilation time has increased a fair bit, as we have focused no effort on optimizing the performance of the compiler. A few obvious places for gains include:

• Ensuring that codegen only happens once (particularly for gocode).
• Parallelizing the compilation process
• Caching parsed workflow specs, rather than reparsing multiple times

[vaastav]

• Ensuring that codegen only happens once (particularly for gocode).
• Parallelizing the compilation process
• Caching parsed workflow specs, rather than reparsing multiple times