introduce Slot newtype for beacon api types

[benluelo]

this has bitten me too many times

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, ssz::Ssz)]
struct Slot(u64);

to match the beacon api specification for slot json ser/de, this type should serialize via string (see

union/lib/serde-utils/src/lib.rs

Lines 512 to 546 in e652dd1

	pub mod string {
	use alloc::string::String;
	use core::{fmt::Display, str::FromStr};
	use serde::{de::Deserialize, Deserializer, Serialize, Serializer};
	pub fn serialize<S, T>(data: T, serializer: S) -> Result<S::Ok, S::Error>
	where
	S: Serializer,
	T: Display + Serialize,
	{
	if serializer.is_human_readable() {
	serializer.collect_str(&data)
	} else {
	data.serialize(serializer)
	}
	}
	pub fn deserialize<'de, D, T>(deserializer: D) -> Result<T, D::Error>
	where
	D: Deserializer<'de>,
	T: FromStr + Deserialize<'de>,
	{
	if deserializer.is_human_readable() {
	String::deserialize(deserializer).and_then(|s| {
	s.parse()
	// TODO fix error situation
	// FromStr::Err has no bounds
	.map_err(|_| serde::de::Error::custom("failure to parse string data"))
	})
	} else {
	T::deserialize(deserializer)
	}
	}
	}

for an example of how, note that it only serializes via string if the de/serializer is human readable).

this type should be added in this file: https://github.com/unionlabs/union/blob/e652dd1905e77d0138fb68b351cb17248d830689/lib/beacon-api-types/src/lib.rs

all fields that represent a slot should be changed to this type.