Set MSRV to 1.70 and remove a few unused dependencies.

[01mf02]

Checklist

• I have read the Contributor Guide
• I have read and agree to the Code of Conduct
• I have added a description of my changes and why I'd like them included in the section below

Description of Changes

This sets an MSRV of 1.70 and decreases the required edition to 2021, making it possible to compile toml-span with older compilers. This enables me in particular to use toml-span in my own project, where I have an MSRV of 1.70 as well.

Furthermore, this removes a few unused dependencies from the workspace, such as syn and quote.

[01mf02]

May I ask if there's something I can do to get this merged? If you are concerned about introducing an MSRV, then I can also remove that. The only thing that I'd really need is the Rust edition; the MSRV is a nice bonus, but I can well live without it.

[Jake-Shadle]

Github won't allow me to push changes to your fork, please apply this diff and I'll merge.

diff --git a/.github/workflows/rust-ci.yml b/.github/workflows/rust-ci.yml
index 49529d2..7d42b67 100644
--- a/.github/workflows/rust-ci.yml
+++ b/.github/workflows/rust-ci.yml
@@ -23,7 +23,7 @@ jobs:
       - name: check rustfmt
         run: |
           rustup component add rustfmt
-          cargo fmt -- --check --color always
+          rustfmt --check --color always --edition 2024 toml-span/src/**.rs
 
       # run clippy to verify we have no warnings
       - run: cargo fetch

[01mf02]

@Jake-Shadle, thank you so much for merging this, and for making the changes to CI (ff1a2a6)! And thanks also for maintaining toml-span --- it has been a breeze to use. :)