fix: correct persistent variable detection with underscores

[Venshard]

Summary

Fixes #532

Fixes a bug in the linter where persistent variables containing multiple underscores (e.g., persistent.show_map_debug) are incorrectly flagged as undefined when they appear at the end of a line or before certain non-alphabetic characters.

The Problem

The rxPersistentCheck regex in src/diagnostics.ts uses a trailing anchor [^a-zA-Z] to identify the end of a persistent variable reference.

const rxPersistentCheck = /\s+persistent\.(\w+)[^a-zA-Z]/g;

Because _ (underscore) is a word character (\w) but not an alphabetic character ([a-zA-Z]), the regex engine backtracks when it encounters an underscore it can't skip, or when the variable is at the end of a line.

Reproduction Case

Consider the following line of code:

persistent.show_map_debug = not persistent.show_map_debug

1. For the first occurrence, the = after the variable satisfies [^a-zA-Z], so it matches show_map_debug correctly.
2. For the second occurrence (at the end of the line), there is no character after debug.
3. The regex engine captures show_map_debug in (\w+), but then fails to find [^a-zA-Z].
4. It backtracks, capturing show_map in (\w+).
5. It then successfully matches the following _ (from _debug) as the [^a-zA-Z] character.
6. Result: The linter thinks the code is referencing persistent.show_map, which hasn't been defined, and throws a warning.

The Fix

Updated the regex to use a positive lookahead (?=[^a-zA-Z0-9_]|$). This ensures that the capture group (\w+) only matches the full identifier by asserting that it is followed by either a non-identifier character (like space, colon, or equals) or the end of the line.

The updated regex is:

const rxPersistentCheck = /\s+persistent\.(\w+)(?=[^a-zA-Z0-9_]|$)/g;

This prevents the regex engine from backtracking and matching partial identifiers (like show_map from show_map_debug) just to satisfy the trailing character requirement.