Incorrect NoQA placement for continuation with multi-line string

[dhruvmanila]

Take the following code snippet:

assert foo, \
    """triple-quoted
    string"""

Running the following command repeatedly:

$ ruff check --no-cache --isolated --select=F821 fstring.py --add-noqa
Added 1 noqa directive.

$ ruff check --no-cache --isolated --select=F821 fstring.py --add-noqa
Added 1 noqa directive.

...

It keeps on adding the noqa directive inside the first line of the string:

assert foo, \
    """triple-quoted  # noqa: F821  # noqa: F821
    string"""

I think the problem is in the way the range is being pushed onto the NoQA mapping in the following code:

ruff/crates/ruff/src/noqa.rs

Lines 764 to 777 in dcbd8ea

	pub(crate) fn push_mapping(&mut self, range: TextRange) {
	if let Some(last_range) = self.ranges.last_mut() {
	// Strictly sorted insertion
	if last_range.end() <= range.start() {
	// OK
	}
	// Try merging with the last inserted range
	else if let Some(intersected) = last_range.intersect(range) {
	*last_range = intersected;
	return;
	} else {
	panic!("Ranges must be inserted in sorted order")
	}
	}

1. The <= doesn't make it strict
2. We should use the union range instead of intersected range

So,

    pub(crate) fn push_mapping(&mut self, range: TextRange) {
        if let Some(last_range) = self.ranges.last_mut() {
            // Strictly sorted insertion
            if last_range.end() < range.start() {
                // OK
            } else if range.end() < last_range.start() {
                panic!("Ranges must be inserted in sorted order")
            } else {
                *last_range = last_range.cover(range);
                return;
            }
        }

        self.ranges.push(range);
    }