refactor(deprecations): type annotations using table proxying

[pynappo]

Introduces a util that creates a new table that "proxies" the original one w/ metatable magic (basically the proxy table is a tree where each node contains the full list of keys to access it, and tree nodes are generated on-demand)

This way we can do some type casting and be able to more easily migrate things like:

local old = proxy.new(config) --[[@as config.old]]
local new = proxy.new(config) --[[@as config]]

-- no need to check intermediate fields when accessing the proxy
if proxy.get(old.deprecated_config_field.nested_field) then
  proxy.set(new.new_config_field.new_nested_field, old.deprecated_config_field.nested_field)
end

Not sure about performance but DX should be way better than typing in dot-delimited string index paths into raw strings with no typing hints