Lists of files or directories to exclude can be specified via comma-separated
environment variables and CLI flags. Values are merged using the append
strategy, so that configuration defaults are extended by environment variables
and finally by the CLI. Whitespace around entries is trimmed and duplicates are
preserved. For example:
DDLINT_IGNORE_PATTERNS=".git/,build/"
mytool --ignore-patterns target/
results in ignore_patterns = [".git/", "build/", "target/"].
By default, the ignore-pattern list includes [".git/", "build/", "target/"].
These defaults are extended (not replaced) by environment variables and CLI
flags via the append merge strategy.