fix(transform): single routing pass via claims; namespace-aware handlers; statement spans on facts

[pyramation]

Summary

Stage 1 of the AST convergence plan (constructive-planning #1323). Three tightly-coupled changes to @pgsql/transform:

1. Fixes a live double-routing bug. Every "the walker does NOT auto-recurse into X" comment in transform.ts is false — @pgsql/traverse tag-synthesizes concrete typed fields (CreateStmt.relation, Constraint.pktable, TypeCast.typeName, CallStmt.funccall, …), verified empirically for all ~24 claimed cases. So each site was routed twice: once by the statement handler, once by the generic child visitor. Idempotent for acyclic mappings, but a cyclic mapping (a→b, b→a) swapped back and the leftover-validator threw:

AST transformation incomplete: found 1 untransformed schema name(s) "a" ...

Fix is a claim registry: each routable site (RangeVar / name-list array / (container, field)) is resolved through the router at most once per result — claimSite(result, site, field) guarded inside transformRelation / transformNameList / transformSchemaNameField / rewriteSchemaField. Since the walker is pre-order, the most context-aware handler claims first (e.g. DropStmt routing ObjectWithArgs.objname with ns function beats the generic ObjectWithArgs visitor's ns unknown).

2. Deletes ~20 redundant statement handlers (pure duplicates of the generic RangeVar/TypeName/FuncCall visitors) and trims partial ones (CreateFunctionStmt return/param type loops, CreateTrigStmt.relation, AlterSeqStmt.sequence, CreateCastStmt type blocks, …). Handlers that carry real context stay — and several now pass their namespace instead of defaulting to unknown:

 AlterOwnerStmt / AlterObjectSchemaStmt / RenameStmt / CommentStmt:
-  transformNameList(node.object..., result)              // ns 'unknown'
+  transformNameList(node.object..., result, namespaceOfObjectType(...))

so object-level routes now apply to ALTER FUNCTION ... OWNER TO, ... SET SCHEMA, RENAME, and COMMENT ON forms (new test: a function-only route rewrites ALTER FUNCTION a.f(int) OWNER TO u).

3. Adds span to StatementFacts:

interface StatementFacts {
  ...
  span: StatementSpan; // { start, len } — parser byte offsets into the classified script
}

sql.slice(span.start, span.start + span.len) is the statement's verbatim source, so downstream consumers (pgpm/slice exclusion, the upcoming PgpmProgramAst statement layer) never need a second parse just to recover locations.

Net: transform.ts shrinks by ~200 lines; 234 tests green (228 existing + 6 new in routing-claims.test.ts); no API changes beyond the additive span field.

Link to Devin session: https://app.devin.ai/sessions/025fb88043964fdbb335ac5e39df2478
Requested by: @pyramation

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