Update the MSRV to 1.81 and the edition to 2021 (#222)

- [x] I agree to follow the project's [code of
conduct](https://github.com/georust/.github/blob/main/CODE_OF_CONDUCT.md).
- [ ] I added an entry to the project's change log file if knowledge of
this change could be valuable to users.
  - Usually called `CHANGES.md` or `CHANGELOG.md`
  - Prefix changelog entries for breaking changes with "BREAKING: "
---

Author: urschrei

.github/workflows/test.yml

@@ -11,7 +11,7 @@ on:
 
 env:
   LIBPROJ_VERSION: 9.4.0
-  RUST_MSRV: "1.75"
+  RUST_MSRV: "1.81"
   RUST_LATEST: "1.83"
 
 jobs:

CHANGES.md

@@ -1,6 +1,7 @@
 ## Unreleased
 
 - Update build status badge
+- Update MSRV to 1.81
 
 ## 0.28.0 - 2024-12-20
 

Cargo.toml

@@ -11,8 +11,8 @@ keywords = ["proj", "projection", "osgeo", "geo"]
 categories = ["science::geo", "api-bindings"]
 license = "MIT OR Apache-2.0"
 readme = "README.md"
-edition = "2018"
-rust-version = "1.75"
+edition = "2021"
+rust-version = "1.81"
 
 [dependencies]
 proj-sys = { version = "0.25.0", path = "proj-sys" }