feat: add ChainId type

[tdelabro]

Add the type ChainId

What is the new behavior?

The ChainId type allows for representing the two starknet chains, SN_MAIN and SN_SEPOLIA.
It offers type conversion from and into Felt, ShortString, String.

A new Rust feature devnet allows adding a custom local devnet with any valid ShortString as name (eg. SN_DEVNET).

Also, add a new short_string! macro, for compile-time creation of ShortStrings

Does this introduce a breaking change?

Yes. Replace TryFrom<&str> for ShortString by FromStr for ShortString.
More idiomatic

[gabrielbosio]

Suggested change

	if value.as_ref() == SN_MAIN_STR {
	ChainId::Mainnet
	} else if value.as_ref() == SN_SEPOLIA_STR {
	ChainId::Sepolia
	} else {
	ChainId::Devnet(value)
	}
	match value.as_ref() {
	SN_MAIN_STR => ChainId::Mainnet,
	SN_SEPOLIA_STR => ChainId::Sepolia,
	_ => ChainId::Devnet(value),
	}

Also, why does conversion from ChainId to ShortString is possible but not the other way around if feature devnet is disabled?

[tdelabro]

It becomes failable when no feature devnet, so we implement TryFrom instead.
See below:
impl TryFrom<ShortString> for ChainId

[gabrielbosio]

So this means that without the devnet feature we only can convert a ShortString to ChainId with try_into and not with into? Even if the ShortString may be SN_MAIN_STR or SN_SEPOLIA_STR