Support golang 1.18 or higher and type parameters

[kuzuha]

Proposed Changes

• Increase minimal supported version from Go 1.15 to Go 1.18
• Bump up to v2
• Support type parameters

Further Comments

Support Go 1.18 Type parameters.

Checklist

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• Under any circumstances, by submitting your contribution, you are deemed to accept and agree to be bound by the terms and conditions of the CLA.

[kuzuha]

@nguyengiabk how do you think about this?

[nguyengiabk]

@kuzuha
Thank you so much for creating a PR.
And so sorry for late response.

Because generics are not production ready as stated here, please give me some time to consider 🙇
For now, could you please put v2 code into v2 sub-folder as recommended by https://go.dev/blog/v2-go-modules?

[nguyengiabk]

@kuzuha
Sorry for late response.
I've talked with some Go experts in our company, and we agreed that this refactoring has limited benefit (no clear reason to do) while reducing the readability. And one more important thing is Go Generics is still not production-ready.
So I will let this PR be open for a while.
We can take a look later when it makes more sense.

[agandreev]

@nguyengiabk Hello! Thank you so much for your library!!
What do you think about adding generics this time? It will be rather convenient for integrate breaker into grpc and http clients