Infer exact rows for #table expressions

[Alex Vallone (amv146)]

Why

PQLS already inferred a schema for static #table calls, but it discarded literal row values. As a result, later operations such as numeric item access, field projection, and table concatenation could not use row data that was known at inspection time.

This PR retains exact rows when it is safe to do so and keeps a schema-only table when the schema is known but the rows are not.

Behavior

Input	Inferred result
#table({"Name"}, {{"Betty"}})	Closed DefinedTable with Name: Any and the exact row
#table(type table [Name = text], rows) with dynamic rows	Schema-only DefinedTable with Name: text
Known columns with malformed, incompatible, or more than 100 rows	Schema-only DefinedTable
Dynamic or open columns	Primitive table

List-form columns continue to use Any; row contents do not infer or widen column types. Explicit type table [...] schemas retain their declared field types, and exact rows are kept only when their values are compatible with those declarations.

Downstream operations

• Numeric item access returns the exact retained row, reports an out-of-range exact index as None, or returns a record derived from the known schema when rows are unavailable.
• Field projection projects both the schema and every retained row. If an open table projects an undeclared field, the field is Any and exact rows are dropped.
• Table concatenation combines closed schemas, unions shared field types, makes one-sided fields nullable, and fills missing row values with null. Exact rows are retained only when both operands have them and the combined total is at most 100 rows; otherwise the combined schema is preserved without rows.
• Operations involving an unknown/open schema or a primitive table operand continue to return primitive table.

For example:

#table(type table [A = number], {{1}})
    & #table(type table [B = text], {{"two"}})

produces a schema equivalent to [A = nullable number, B = nullable text] and exact rows equivalent to {[A = 1, B = null], [A = null, B = "two"]}.

Non-goals

Inferring column types from list-form row contents is intentionally deferred to a follow-up change.

Dependency

This uses @microsoft/powerquery-parser@2.0.0, where DefinedTable.rows is optional: omitted rows mean "schema known, rows unknown," while [] means an exact empty table.

Validation

• npm ci --registry https://registry.npmjs.org
• npm run build
• npm run lint
• npm test (776 passing)