chore: add PR template #354

Job	Run time
rust-library-base / Feature Checks	2m 40s
rust-library-base / Base Checks / Docs	2m 31s
rust-library-base / Base Checks / Clippy	2m 41s
rust-library-base / Base Checks / Rustfmt	40s
rust-library-base / Base Checks / Test Suite	6m 2s
rust-library-base / Base Checks / doctest	3m 4s
	17m 38s

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