Using pointer address as node/symbol id

Nodes and symbols currently store an atomic integer representing their ID, which is lazily assigned upon first use. I was playing with using the pointer addresses as their ID, reducing the size of those structures and avoiding atomic reads on access.

```go
func GetNodeId(node *Node) NodeId {
return NodeId(uint64(uintptr(unsafe.Pointer(node))))
}

func GetSymbolId(symbol *Symbol) SymbolId {
return SymbolId(uint64(uintptr(unsafe.Pointer(symbol))))
}
```

A potential downside is that `KeyBuilder` will observe larger numbers, requiring additional bytes to represent various keys. It may also affect ordering as IDs will no longer be strictly increasing, but I believe this shouldn't matter given that ID assignment is already non-deterministic.

A quick attempt passes the `hereby test` and shows a slight reduction in overall memory usage, but I don't have good insight into actual performance benfits/downsides of this approach.

I am opening this as issue instead of PR to discuss, possibly to learn this has been considered and may have been rejected for some reason. I'd be happy to open a PR if desired.

Start by reading the GetNodeId and GetSymbolId examples, then inspect how KeyBuilder represents IDs. Run hereby test to reproduce the reported baseline; the issue does not define acceptance criteria beyond discussing memory, performance, key size, and ordering effects.

Written by the indexing model from the issue text.