Fix SQL name transforms failing on JSON arrays that contain null - #9825

Statement.defaultTransforms backs transformResultNames, and also the sql.json handling of transformQueryNames in @effect/sql-pg and @effect/sql-pglite. It read constructor from the first item of every array and treated every later item as an object:

const transforms = Statement.defaultTransforms(String.snakeToCamel)

transforms.array([{ user_id: 1, posts: [null] }])
// TypeError: Cannot read properties of null (reading 'constructor')

transforms.array([{ user_id: 1, tags: [{ tag_name: "admin" }, null] }])
// TypeError: Cannot convert undefined or null to object

transforms.array([{ user_id: 1, tags: [{ tag_name: "admin" }, 1, "ops"] }])
// [{ userId: 1, tags: [{ tagName: "admin" }, {}, { "0": "o", "1": "p", "2": "s" }] }]

PostgreSQL's json_agg returns [null] for an empty LEFT JOIN group. @effect/sql-pg parses json columns and applies nested transforms by default, so with transformResultNames set such a query dies with the first TypeError. With transformQueryNames set, compiling sql.json([null]) throws the same error.

Array items that are not objects are now kept as they are. As before, the first item decides whether an array is transformed at all, so arrays of dates, numbers or strings are returned unchanged.

The test in packages/effect/test/sql/Statement.test.ts covers [null] and mixed object/null/scalar arrays for both the nested and flat transforms.

Validation: pnpm vitest run packages/effect/test/sql/Statement.test.ts passes (11 tests) and the new test fails without the fix. pnpm lint and tsc -b for packages/effect pass.

Closes EFF-2841

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