Packages under users should merge with fallback registries

[ayuka]

Here's our current situation:

• We have packages released on the public Wally registry under user/
• We also have packages released on a private Wally registry under user/
• We do not re-publish the public packages on the private one, instead using the fallback registries to cover this.

Unfortunately, the LSP only recognizes packages released in our private registry and shows an error for packages under the private registry. It would be nice for the LSP to merge together packages under the same user in fallback registries.