Add msrv definitions to common and crypto

This will effectively add msrv protections to the entire project as almost
everything grabs from these.

Doesn't add msrv to coins as coins/bitcoin is still frozen.

Doesn't add msrv to services since cargo msrv doesn't play nice with anything
importing the runtime.

crypto/multiexp/Cargo.toml

@@ -7,6 +7,7 @@ repository = "https://github.com/serai-dex/serai/tree/develop/crypto/multiexp"
 authors = ["Luke Parker <lukeparker5132@gmail.com>"]
 keywords = ["multiexp", "ff", "group"]
 edition = "2021"
+rust-version = "1.70"
 
 [package.metadata.docs.rs]
 all-features = true
@@ -31,7 +32,7 @@ k256 = { version = "^0.13.1", default-features = false, features = ["arithmetic"
 dalek-ff-group = { path = "../dalek-ff-group" }
 
 [features]
-std = ["std-shims/std"]
+std = ["std-shims/std", "zeroize/std"]
 
 batch = ["rand_core"]