Improve derivation path checking logic

[lrettig]

It's not 100% clear whether this logic belongs here, or whether the caller should implement it (and this lib should be more unopinionated). Either remove it, and make sure similar logic is called downstream, or else clean this up (move it into the derivation-path crate and bake it into the type).

spacemesh-sdk/ed25519-bip32/src/lib.rs

Lines 68 to 89 in 19feebb

	// for now we are rather strict with which types of paths we accept, to avoid errors and to
	// be as compatible as possible with BIP-44. the path must be of the format
	// "m/44'/540'/...", i.e., it must have purpose 44 and coin type
	// 540 and all path elements must be hardened. we expect it to contain between 2 and 5
	// elements.
	if derivation_path_inner.path().len() < 2 {
	err!("path too short");
	}
	if derivation_path_inner.path().len() > 5 {
	err!("path too long");
	}
	if derivation_path_inner.path()[0].to_u32() != 44 {
	err!("bad path purpose");
	}
	if derivation_path_inner.path()[1].to_u32() != 540 {
	err!("bad path coin type");
	}
	for p in derivation_path_inner.path() {
	if !p.is_hardened() {
	err!("path isn't fully hardened");
	}
	}