feat[lang]: improve error message for namespace collision

[stoyanov-kaloyan]

Added improved error message for namespace collisions in imports

resolves #4579

New error message looks like:

Error compiling: _test.vy
vyper.exceptions.NamespaceCollision: 'math' has already been declared via import (alias=`math`).

 Suggested fix: rename or remove the previous declaration (e.g. use `import math as ...` to avoid collisions)

  contract "_test.vy:2", line 2:0 
       1 from snekmate.utils import math
  ---> 2 import math
  -------^

Commit message:

feat[lang]: improve error message for namespace collision

Description for the changelog

Added a block in which it attempts to provide an easier to read hint for the user.

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