Fix djlint:off formatting not being respected inside script tags

[Copilot]

The {# djlint:off #} directive was not being respected when used inside <script> tags, causing JavaScript code within ignore blocks to be formatted anyway. This could break JavaScript syntax and functionality.

Problem:

<script>
{# djlint:off #}
function test() {
    var x = 1;
        var y = 2;  // This bad indentation got "fixed" incorrectly
}
{# djlint:on #}
function other() {
    var a = 1;
    var b = 2;
}
</script>

The root cause was in src/djlint/formatter/js.py where the launch_formatter function only checked if the entire script tag was within an unformatted block using child_of_unformatted_block(), but didn't detect unformatted blocks within the script content itself.

Solution:
Enhanced the JavaScript formatter to:

1. Detect {# djlint:off #} blocks within script content using the same regex patterns as the rest of djLint
2. Preserve unformatted sections while still formatting the remaining JavaScript code
3. Handle multiple ignore blocks within a single script tag
4. Maintain backward compatibility for scripts that are entirely within ignore blocks

After the fix:

<script>
{# djlint:off #}
function test() {
    var x = 1;
        var y = 2;  // Bad indentation preserved ✅
}
{# djlint:on #}
function other() {
    var a = 1;      // Still formatted properly ✅
    var b = 2;
}
</script>

The fix properly filters out empty regex matches and uses the correct flags (RE_FLAGS_IMSX) for pattern matching with verbose regex expressions.

Fixes #868.

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