gnovm: support for /internal/ subfolders

[moul]

We need an equivalent of Go's /internal/ feature in Gno, where an internal path can only be imported by its parent folders.

Details

• Internal Path: Should only be importable by the parent folder.
• Chain Calls: Should be callable by the chain from GnoSDK.
• maketx call: Still undecided if maketx call should be allowed to call internal packages (currently leaning towards no).
• Read-Only Support: Should support read-only reading with q_eval.