Unify single-node and bulk deployment validation paths

[shangyian]

Summary

Single-node validate and bulk deployment historically ran two separate validators that gave different verdicts for the same SQL. This branch adds validate_node_data_v2 alongside the legacy validator, built on the same validate_node_query primitive deployment uses, and wires it into POST /nodes/{name}/validate/.

Shared primitives are called by both extract_node_graph (deployment) and validate_node_data_v2 (single-node), so candidate extraction and parent/missing classification produce identical results from both directions. The deployment path now also emits MissingParent records for unresolved ast.Table refs (matching single-node behavior) and filters non-metric resolutions out of derived-metric parent lists.

Validation changes on v2 over legacy:

• Ambiguous unqualified column refs across joins are flagged (e.g., SELECT col FROM a JOIN b ON a.col = b.col where col lives on both)
• EXPLODE(array<struct<a, b>>) AS (c1, c2): struct fields unpack positionally, both in LATERAL VIEW and projection forms
• CROSS JOIN UNNEST(t.arr) AS u(x): UNNEST sees the left-side table in scope; struct unpacking and POSEXPLODE handled
• Supports from-less series-generator pattern SELECT … LATERAL VIEW EXPLODE(sequence(1, N)) AS x
• Multiple LATERAL VIEW EXPLODE(…) AS c in one select no longer collide on the default alias
• VALUES (NULL, 'a'), ('x', 'b') AS t(c1, c2): column type comes from the first typed row, not any given null
• arr[1] on a ListType column resolves to the element type
• from_json(string_col, 'MAP<STRING, STRING>') resolves its return type so downstream references work
• col.field struct access on a deep chain resolves correctly
• When EXPLODE's arg references a missing column, the real Column X not found cause surfaces alongside the downstream Unable to infer type noise

Test Plan

Two fixture bugs surfaced and fixed.

• PR has an associated issue: #
• make check passes
• make test shows 100% unit test coverage

Deployment Plan

[netlify]

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