Import error for VyperException on ast.py

[salustiana]

The import path for VyperException is wrong, causing the lsp to crash at launch on neovim.

[ERROR][2025-03-19 14:10:49] .../vim/lsp/rpc.lua:770 "rpc" "vyper-lsp" "stderr" " File \"/home/salus/si/contracts/.venv/lib/python3.13/site-packages/vyper_lsp/main.py\", line 33, in <module>\n from vyper_lsp.handlers.signatures import SignatureHandler\n File \"/home/salus/si/contracts/.venv/lib/python3.13/site-packages/vyper_lsp/handlers/signatures.py\", line 14, in <module>\n from vyper_lsp.ast import AST\n File \"/home/salus/si/contracts/.venv/lib/python3.13/site-packages/vyper_lsp/ast.py\", line 12, in <module>\n from vyper.utils import VyperException\nImportError: cannot import name 'VyperException' from 'vyper.utils' (/home/salus/si/contracts/.venv/lib/python3.13/site-packages/vyper/utils.py)\n"

This PR fixes it: #15