Stop using pointer receiver on *Version about semver

[sdboyer]

A slightly more detailed explanation of the performance issue:

With the way that go's escape analysis works, creating and returning a pointer value from outside of the scope in which it was created will always result in a heap allocation. (Go's escape analysis is not very sophisticated right now). Avoiding small allocations are one of the first and major things you do to improve runtime performance - see, for example, this ol' Cloudflare piece.

Moreover, because of the typical use pattern for a version, you also get bit on GC. It's not uncommon - say, in vsolver - to create lots of *Version instances, even just ephemeral ones as part of a larger calculation. (The 2.x branch of this lib does this internally as well, with the new constraint calculation system.) This means creating lots of typically short-lived, small (almost always <100 bytes, often only 24 bytes), heap-allocated values. All of those become extraneous garbage that the GC has to deal with.

And, really, this is an easy win, because there's no intrinsic need for versions to be heap allocated. They consistent entirely of stack-allocable components - three int64s, and three immutable strings. If people want to use this library as a component in a serious, larger, and especially long-lived application, it shouldn't make allocations it doesn't have to, or make a needless mess for GC to clean up.

[mattfarina]

@sdboyer thanks for providing the detail and those pointers (pun intended).

[mattfarina]

Closing because this has been merged.