ci: Improve GitHub Actions config

[notpeter]

• Remove deprecated actions-rs/toolchain and actions-rs/cargo
• Add caching with Swatinem/rust-cache
• On run CI for pushes to main or branches with a PR.
• Add cancel keys so only new commit on PR branch supercedes previously running builds.
• Remove unnecessary "permissions: {contents: read}"; this is default for builds on push/pull_request.
• Switch release to matrix build
• Add support for draft release testing in PRs (release-test label)
• Pin to rust 1.93.1 in rust-toolchain.toml because clippy complains in 1.94.0
• Add macOS Intel release

Workflow	Before (uncached)	After (cached)
build.yml	6m48s	-
release.yml windows	5m11s	2m7s
release.yml linux	2m21s	49s
release.yml macos	2m15s	58s
test.yml	4m38s	2m30s
PR Minimum	6m48s	2m30s

[notpeter]

Pinned to 1.93.1 because clippy on 1.94.0 complains:

    Checking rfd-github v0.1.0 (/home/runner/work/rfd-api/rfd-api/rfd-github)
error: the `Err`-variant returned from this closure is very large
   --> rfd-github/src/lib.rs:257:23
    |
 39 |       ClientError(#[from] ClientError),
    |       -------------------------------- the largest variant contains at least 128 bytes
...
257 |               .and_then(|committer| {
    |  _______________________^
258 | |                 committer
259 | |                     .date
260 | |                     .parse::<DateTime<Utc>>()
261 | |                     .map_err(GitHubError::InvalidDate)
262 | |             })?;
    | |_____________^
    |
    = help: try reducing the size of `GitHubError`, for example by boxing large elements or replacing it with `Box<GitHubError>`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.94.0/index.html#result_large_err
    = note: `-D clippy::result-large-err` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::result_large_err)]`

error: the `Err`-variant returned from this closure is very large
   --> rfd-github/src/lib.rs:339:27
    |
 39 |       ClientError(#[from] ClientError),
    |       -------------------------------- the largest variant contains at least 128 bytes
...
339 |                   .and_then(|committer| {
    |  ___________________________^
340 | |                     committer
341 | |                         .date
342 | |                         .parse::<DateTime<Utc>>()
343 | |                         .map_err(GitHubError::InvalidDate)
344 | |                 })?;
    | |_________________^
    |
    = help: try reducing the size of `GitHubError`, for example by boxing large elements or replacing it with `Box<GitHubError>`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.94.0/index.html#result_large_err