Avoid repeated type creation

Cache int singleton creation

Use new api in CompilerTypeTestApi

Extract out the which semtype implementation used for tests

Implement semtype tests

Fix doc comments

Avoid doing a `instanceOf` on a abstract type (which trigger a full type
check) and instead use a virtual function that create the basic type
which should be cheaper

Memoization depends on hash and equals. Otherwise we create duplicate memos for equal types

Widened type for basic types is the basic type where as for other types it is contextually expected type (not the actual shape of the value). This is to avoid the overhead of having to create singleton types for each basic type value

Due to reasons that are not entierly clear to me when we run all the
unit tests some how types from `record_project_closed_rec_equiv` to
clashed with types defined in other unit tests. As a temperary
workaround I introduced a new package name for this.