triedb/pathdb: implement trienode history indexing scheme

[rjl493456442]

This PR implements the indexing scheme for trie node history. Check #33399 for more details

[MariusVanDerWijden]

LGTM, I like the chunking scheme, took me a bit to understand, but I think we discussed it in a call before. Added a few suggestions, but more like nitpicks

[MariusVanDerWijden]

We can use the builtin clear(b.index) clear(b.ext) here, then we can use the builtin "maps" package instead of the /x/exp/maps package

[rjl493456442]

I can change it in the following PR, just don't want to lose your approval.

[MariusVanDerWijden]

I think it would be nice to have a test for the iterator function, just to make sure that the correct amount of elements etc are returned

[rjl493456442]

It's a bit hard to come up with a solid test to verify the elements yielded by iterator, as we only expect the "touched chunks" by a set of dirty nodes.

I will definitely add it back, it's a valuable test case.

[MariusVanDerWijden]

Why can the path not be longer than 3?
Wouldn't it be easier to hardcode it then?
e.g.
switch len(path)
case 3:
offset *= 16
value = value *16 + bytes[2]
fallthrough
case 2:
offset = 16
value = value16 + bytes[1]
fallthrough
case 1:
offset = 16
value = value16 + bytes[0]

or something like this? Maybe its a bit easier to understand

[MariusVanDerWijden]

Or maybe something like this:

// The numeric node ID is represented by the uint16 with the assumption the length
// of path won't be greater than 3.
func hexPathNodeID(path string) uint16 {
	bytes := []byte(path)
	n := len(bytes)

	// Pre-computed offsets for paths of length 0, 1, 2, 3:
	// length 0: 0
	// length 1: 1
	// length 2: 1 + 16 = 17
	// length 3: 1 + 16 + 256 = 273
	var offset uint16
	switch n {
	case 3:
		offset += 256
		fallthrough
	case 2:
		offset += 16
		fallthrough
	case 1:
		offset += 1
	default:
	}

	// Compute value from hex digits
	var value uint16
	for i := 0; i < n; i++ {
		value = value*16 + uint16(bytes[i])
	}

	return offset + value
}

[rjl493456442]

The path here refers to the "inner" path suffix within the chunk. As I only select the consecutive 3 levels as a chunk, with at most 273 nodes in a chunk, so the assumption is implicitly held.