ci: add `cargo-msrv` to jobs

style(clippy): make getter into const fn

ci: ensure correct macro crate ver being re-exported

ci: split into several jobs

fix: use shared workspace version for all crates

style(cargo-deny): permit unicode licenses

chore: bump version to 0.3.0

test: lifetimes and generics in err ty

feat: support generics + lifetimes in error types

chore: bump ver to 0.3.0-rc.2

fix: use no_std attr

chore: bump versions to 0.3.0-rc.1

docs(README): mention `#![no_std]`

feat: no_std support

fix: pin version and mention in docs