refactor(cache): simplify noCache condition

[agilgur5]

Summary

Greatly simplify the noCache condition in tscache -- basically most of the code is not used and can be removed or can early return in the case that there is no cache.

• This builds on top of refactor(cache): simplify clean method #358 's simplifications

Details

• if there is no cache, we don't need to do any operations on a cache at all, so we can just totally skip all the cache operations and return early

  • this should be a perf improvement, at the very least on memory usage, as lots of stuff isn't created or processed now
    • this may make clean: true a more optimal choice for smaller projects, as the FS usage when writing to cache may be slower than the small amount of compilation and type-checking required in small projects

• to start, from the constructor, the only necessary piece when noCache is the dependency tree

  • this is needed for walkTree and setDependency to function, but otherwise is unused when noCache
    • this might be able to be further optimized to remove the graph entirely when noCache, but that is saved for potential future work and not part of this PR
  • so, we can just move the tree creation further up in the constructor as its previous ordering within the constructor does not actually matter
  • once this is done, we can just early return when noCache instead of doing all the cache-related actions, since they're not needed when there is no cache
    • no need to set cacheDir or any hashes etc since they're not used
      • note that clean only uses cachePrefix and cacheRoot, which are already set, and does not use cacheDir
    • no need to init the cache as it's not used
      • also slightly change the ordering to move init right after its prereqs are done, i.e. setting cacheDir, hashOptions, etc
        • just keeps with the flow instead of calling it in the middle of the ambient type processing
    • no need to check ambient types as that is only used for cache invalidation (marking things dirty), which is not used when there is no cache
      • note that isDirty is literally never called when noCache

• from there, since we don't call checkAmbientTypes or init when noCache (the constructor is the only place they are called and they are both private), we can entirely remove their noCache branches

  • fairly simple for checkAmbientTypes, we just remove the tiny if block that sets ambientTypesDirty, as, well, "dirty" isn't used when there is no cache
  • for init, this means we can entirely remove the creation of NoCache, which isn't needed when there is no cache
    • that means we can also remove the implementation and tests for NoCache
      • and the reference to it in CONTRIBUTING.md

• in done (which is public), we can also simply skip rolling caches and early return when there is no cache

• the only other tiny change is the non-null assertions for ambientTypes and cacheDir

  • this matches the existing, simplifying non-null assertions for all the caches, so I did not workaround that
    • could set a default of an empty array for ambientTypes etc to workaround this, but thought it better to match existing code style and not add new things
  • this also matches the behavior, as while ambientTypes and cacheDir could be null, this is only if there is no cache, in which case, they are never used

Potential Future Work

• Further optimize noCache by exploring if the whole dependencyTree could be removed in that case
• Potentially add heuristics for clean, as it actually may be more performant in the case of smaller projects
  • This would need some perf testing as well