Bug: parseTree silently ignores showingMissingTokens parameter

[leogdion]

Description

In Sources/TokenVisitor/TreeNodeProtocol+Extensions.swift, parseTree(from:withFileName:showingMissingTokens:) hardcodes showMissingTokens: false when constructing TokenVisitor, silently discarding the caller-supplied value.

Fix

Forward the parameter instead of hardcoding:

let visitor = TokenVisitor<Self>(
    locationConverter: ...,
    showMissingTokens: showingMissingTokens  // was hardcoded false
)