refactor(array): deprecate the one-off scalar and validity accessors

[joseph-isaacs]

Summary

Stacked on #9843, which adds the probe API. That PR left the one-off accessors in place with TODO(joe): deprecate this and FIXME: Deprecate scalar_at once encodings have migrated; this one discharges those markers.

A probe performs the same bounds and validity checks as the one-off accessors but can retain encoding preparation across lookups, which a one-shot call cannot. Deprecating the one-off spellings points callers at the replacement without removing anything yet.

Changes

Deprecations. execute_scalar, is_valid and is_invalid on both ArrayRef and Array<V>; OperationsVTable::scalar_at in favour of probe_scalar, whose default still forwards to it during migration. The already-deprecated scalar_at notes named execute_scalar, so they are repointed at probe.

Array::<V>::probe. Array<V> derefs to the encoding data rather than to ArrayRef, so the typed handle had no probe for the deprecation notes to name.

Validity::probe. Validity had no equivalent of ArrayRef::probe — the only ValidityProbe a caller could reach came from ProbeAccess::validity inside an encoding's probe_scalar — so Validity::execute_is_valid and execute_is_null had no replacement to point at. Validity::probe takes the same ProbeUsage and returns an owned ValidityProbe: constant states answer from the variant, Validity::Array reads through an owned ArrayProbe. ValidityProbe gains an Owned access variant and execute_is_valid/execute_is_invalid. Its len becomes optional, so a probe borrowed from a parent still bounds-checks against the source array while one built from a bare Validity relies on the inner probe — matching what Validity::execute_is_valid does today. With that in place, both validity accessors are deprecated too; the replacement for a null check is execute_is_invalid, matching ArrayRef::is_invalid rather than the old is_null spelling.

416 #[expect(deprecated)] annotations across 191 files. CI runs clippy with -D warnings, so the deprecations have to be suppressed somewhere. Annotating each site rather than allowing the lint globally keeps every suppression visible in the code that needs it, and expect rather than allow means the annotation goes unfulfilled once that caller moves to probe — the lint then points at the line to delete.

Sites were located by the compiler, not by grep: each crate checked with --all-targets --all-features, deprecated diagnostics parsed from the JSON output, and an annotation placed on the enclosing item. Three cases need something other than the enclosing function:

• #[rstest] discards lint attributes from its expansion — attributes between #[case] and fn, above #[rstest], inside the body, and on individual statements all leave the warning firing. Those 9 files take a #[expect(deprecated)] at file or mod tests scope.
• A macro_rules! body is linted at its definition site, so the annotation belongs in the macro. One inside assert_nth_scalar! clears the warnings it was causing in five downstream encoding crates.
• A deprecated item using another deprecated item still warns, so scalar_at and is_invalid carry their own annotation.

Commits are split so the deprecations can be reviewed separately from the annotation churn, and so the annotation commits can be dropped wholesale once callers migrate.

API Changes

Deprecations only — nothing is removed and no behavior changes. Additive: Array::<V>::probe, Validity::probe, and ValidityProbe::{execute_is_valid, execute_is_invalid}.

Two items were considered and deliberately left alone: ArrayRef::all_valid/all_invalid are whole-array stats queries rather than per-row access, and Python's Array.scalar_at is a different audience with no probe exposed.

Verification

• cargo check --all-targets --all-features on 28 crates: deprecated=0 unfulfilled=0 errors=0.
• cargo +nightly-2026-09-10 fmt --all --check clean.
• cargo clippy --all-targets --all-features -- -D warnings clean on vortex-array, vortex-fastlanes, vortex-parquet-variant, vortex-spatial, vortex-fuzz, vortex-pco, vortex-zstd, vortex-fsst, vortex-alp.
• cargo test --doc -p vortex-array covers the new Validity::probe example.

Not verified: vortex-duckdb needs libduckdb, which was unavailable in this environment. Its 3 annotated sites (exporter/run_end.rs, two in duckdb/vector.rs) were placed by reading the code rather than from a compiler diagnostic, and are the only ones in the PR not confirmed by a build. Clippy was run on the heaviest crates only; the rest had cargo check.

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