build: declare Rust 1.91 as the minimum version

Duration::from_mins needs it, and without the field cargo on an older
toolchain fails on the edition instead of naming the version it wants.

Cargo.toml

@@ -6,6 +6,7 @@ resolver = "2"
 version = "19.0.0"
 authors = ["Michel de Graaf"]
 edition = "2024"
+rust-version = "1.91"
 license = "MIT"
 repository = "https://github.com/michel/soulseek-rs"
 homepage = "https://re-invention.nl/soulseek-rs/"

soulseek-rs-lib/Cargo.toml

@@ -3,6 +3,7 @@ name = "soulseek-rs-lib"
 version.workspace = true
 authors.workspace = true
 edition.workspace = true
+rust-version.workspace = true
 license.workspace = true
 repository.workspace = true
 homepage.workspace = true

soulseek-rs/Cargo.toml

@@ -3,6 +3,7 @@ name = "soulseek-rs"
 version.workspace = true
 authors.workspace = true
 edition.workspace = true
+rust-version.workspace = true
 license.workspace = true
 repository.workspace = true
 homepage.workspace = true