Fix NOT BETWEEN compiling to the same filter as BETWEEN in metrics SQL

[nishantmonu51]

• parseBetween in runtime/metricsview/metricssql/filter_parser.go ignored the AST's Not flag, so x NOT BETWEEN 1 AND 10 compiled to the same expression as x BETWEEN 1 AND 10 — the range filter was silently inverted.
• Now NOT BETWEEN compiles to (x < low OR x > high); plain BETWEEN output is unchanged.
• Added TestParseFilter cases for both forms.

Steps to reproduce:

1. Call metricssql.ParseFilter("x NOT BETWEEN 1 AND 10") (or use the filter in any metrics SQL WHERE clause).
2. Before this fix it returned {op: and, [{gte, x, 1}, {lte, x, 10}]} — identical to x BETWEEN 1 AND 10, so every row the filter was meant to exclude was included and vice versa.
3. With this fix it returns {op: or, [{lt, x, 1}, {gt, x, 10}]}.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!