Regroup CI testing (#3049)

Part of https://github.com/neondatabase/neon/pull/2410 and
https://github.com/neondatabase/neon/pull/2407

* adds `hashFiles('rust-toolchain.toml')` into Rust cache keys, thus
removing one of the manual steps to do when upgrading rustc
* copies Python and Rust style checks from the `codestyle.yml` workflow
* adjusts shell defaults in the main workflow
* replaces `codestyle.yml` with a `neon_extra_builds.yml` worlflow

The new workflow runs on commits to `main` (`codestyle.yml` was run per
PR), and runs two custom builds on GH agents:

* macos-latest, to ensure the entire project compiles on it (no tests
run)

There were no frequent breakages on macOs in our builds, so we can check
it rarely without making every storage PR to wait for it to complete.
The updated mac build use release builds now, so presumably should work
a bit faster due to overall smaller files to cache between builds.

* ubuntu-latest, without caches, to produce full compilation stats for
Rust builds and upload it as an artifact to GitHub

Old `clippy build --timings` stats were collected from the builds that
use caches and incremental calculation hence never could produce a full
report, it got removed.

rust-toolchain.toml

@@ -4,7 +4,7 @@
 # version, we can consider updating.
 # See https://tracker.debian.org/pkg/rustc for more details on Debian rustc package,
 # we use "unstable" version number as the highest version used in the project by default.
-channel = "1.62.1" # do update GitHub CI cache values for rust builds, when changing this value
+channel = "1.62.1"
 profile = "default"
 # The default profile includes rustc, rust-std, cargo, rust-docs, rustfmt and clippy.
 # https://rust-lang.github.io/rustup/concepts/profiles.html