Wire the smoothed / anchored range-selector modifiers (grammar productions for existing stub tokens) #1

Summary

smoothed / anchored range-selector modifiers parse-fail, e.g. increase(metric[1m] smoothed) → invalid promql query. Both are recent Prometheus range-vector modifiers.

Current state (verified on asap @ c51beaf)

The tokens exist but are wired to nothing:

• src/parser/token.rs: ("smoothed", T_SMOOTHED), T_SMOOTHED => "smoothed" — the lexer recognizes them.
• src/parser/promql.y:124: %expect-unused 'SMOOTHED' 'ANCHORED' — declared as tokens no production consumes.

This is inherited verbatim from GreptimeTeam upstream main, which also stubs them with the same %expect-unused line. So this is not a mirror/rebase away — upstream has not wired them either.

Work

• Add a grammar production consuming SMOOTHED / ANCHORED on matrix_selector (and subquery_expr), removing them from %expect-unused.
• Add an AST field on the matrix/subquery selector to carry the modifier.
• The lexer/token half is already done.

Corpus impact

61 rejections in the ASAPController PromQL corpus. Closest-to-done of the grammar gaps, since the token layer exists.

Constraint

All changes land on the asap branch. Do not sync or PR against GreptimeTeam upstream.