build: use lighter poetry-core

[branchvincent]

👋 Thanks for iredis, very happy user here!

Just noticed the project is still using the full poetry package as its build backend. There's now a preferred, lightweight poetry-core package. What's the benefit? To quote the project's readme:

Prior to the release of version 1.1.0, Poetry was a build as a project management tool that included a PEP 517 build backend. This was inefficient and time consuming in majority cases a PEP 517 build was required... This makes PEP 517 builds extremely fast for Poetry managed packages.

[laixintao]

Thanks! I didn't notice that. let me try.