rust: Set MSRV to 1.59

One of our dependencies uses a feature added in 1.59.0.

docs/Setup.md

@@ -14,7 +14,7 @@ Start by making sure the command line with Gradle works first, because **all the
     1. Install JVM 11 or greater on your system.  Our setup has been tested with Java 11-17.  Although a variety of JVM distributions are available and should work, we have settled on recommending [Adoptium/Temurin](https://adoptium.net), because this is the default distribution used by Gradle toolchains.  For Windows or Linux, be sure that the `JAVA_HOME` environment variable points to the right Java version.  Note: If you switch from a newer to an older JVM version, you may see an error like the following `> com.android.ide.common.signing.KeytoolException: Failed to read key AndroidDebugKey from store "~/.android/debug.keystore": Integrity check failed: java.security.NoSuchAlgorithmException: Algorithm HmacPBESHA256 not available`.  A solution is to delete the debug keystore and allow it to be re-generated.
     1. Android Studio has an embedded JVM, although running Gradle tasks from the command line requires a separate JVM to be installed.  Our Gradle scripts are configured to use toolchains to automatically install the correct JVM version.
 1. Configure Rust
-    1. [Install rust](https://www.rust-lang.org/learn/get-started)
+    1. [Install Rust](https://www.rust-lang.org/learn/get-started). You will need Rust 1.59 or greater. If you install with `rustup` then you are guaranteed to get a compatible Rust version. If you use system packages, check the provided version.
         1. macOS with Homebrew
             1. `brew install rustup`
             1. `rustup-init`

sdk-lib/Cargo.toml

@@ -8,6 +8,7 @@ authors = [
 description = "JNI backend for the Android wallet SDK"
 publish = false
 edition = "2018"
+rust-version = "1.59"
 
 [dependencies]
 android_logger = "0.11"