Bump the MSRV to 1.62 and using #[derive(Default)] on enums (#3304)

## Issue Addressed

N/A

## Proposed Changes

Since Rust 1.62, we can use `#[derive(Default)]` on enums. ✨ 

https://blog.rust-lang.org/2022/06/30/Rust-1.62.0.html#default-enum-variants

There are no changes to functionality in this PR, just replaced the `Default` trait implementation with `#[derive(Default)]`.

testing/ef_tests/src/bls_setting.rs

@@ -2,20 +2,15 @@ use self::BlsSetting::*;
 use crate::error::Error;
 use serde_repr::Deserialize_repr;
 
-#[derive(Deserialize_repr, Debug, Clone, Copy)]
+#[derive(Deserialize_repr, Debug, Clone, Copy, Default)]
 #[repr(u8)]
 pub enum BlsSetting {
+    #[default]
     Flexible = 0,
     Required = 1,
     Ignored = 2,
 }
 
-impl Default for BlsSetting {
-    fn default() -> Self {
-        Flexible
-    }
-}
-
 impl BlsSetting {
     /// Check the BLS setting and skip the test if it isn't compatible with the crypto config.
     pub fn check(self) -> Result<(), Error> {