no-std support for monero-serai (#311)

* Move monero-serai from std to std-shims, where possible

* no-std fixes

* Make the HttpRpc its own feature, thiserror only on std

* Drop monero-rs's epee for a homegrown one

We only need it for a single function. While I tried jeffro's, it didn't work
out of the box, had three unimplemented!s, and is no where near viable for
no_std.

Fixes #182, though should be further tested.

* no-std monero-serai

* Allow base58-monero via git

* cargo fmt

coins/monero/src/ringct/bulletproofs/core.rs

@@ -1,4 +1,4 @@
-use std_shims::sync::OnceLock;
+use std_shims::{vec::Vec, sync::OnceLock};
 
 use rand_core::{RngCore, CryptoRng};