Fix new clippy lints (#2036)

## Issue Addressed

NA

## Proposed Changes

Fixes new clippy lints in the whole project (mainly [manual_strip](https://rust-lang.github.io/rust-clippy/master/index.html#manual_strip) and [unnecessary_lazy_evaluations](https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_lazy_evaluations)). Furthermore, removes `to_string()` calls on literals when used with the `?`-operator.

crypto/bls/src/macros.rs

@@ -95,8 +95,8 @@ macro_rules! impl_from_str {
         type Err = String;
 
         fn from_str(s: &str) -> Result<Self, Self::Err> {
-            if s.starts_with("0x") {
-                let bytes = hex::decode(&s[2..]).map_err(|e| e.to_string())?;
+            if let Some(stripped) = s.strip_prefix("0x") {
+                let bytes = hex::decode(stripped).map_err(|e| e.to_string())?;
                 Self::deserialize(&bytes[..]).map_err(|e| format!("{:?}", e))
             } else {
                 Err("must start with 0x".to_string())

crypto/eth2_wallet/src/wallet.rs

@@ -202,7 +202,7 @@ impl Wallet {
             .json
             .nextaccount
             .checked_add(1)
-            .ok_or_else(|| Error::PathExhausted)?;
+            .ok_or(Error::PathExhausted)?;
 
         Ok(keystores)
     }