Add detection for outer DECLARE statements and update documentation

[max-ostapenko]

• Implemented hasOuterDeclare function to check for outer level DECLARE statements in SQL.
• Updated autoAssignActions to skip operations with outer DECLARE.
• Enhanced README and Copilot instructions to clarify limitations of automated assignment.
• Added tests for various scenarios involving outer DECLARE statements.

[Copilot]

Pull request overview

This PR adds detection for outer-level DECLARE statements in SQL operations to prevent syntax errors when prepending reservation SET statements. BigQuery requires DECLARE to be the first statement in a script, so prepending SET @@reservation before an outer DECLARE would cause the query to fail. The PR implements automatic detection and skipping of such operations.

Changes:

• Added hasOuterDeclare() function to detect DECLARE statements at the outer level of SQL queries, stripping comments to find the first real statement
• Updated applyReservationToAction() to skip reservation assignment for operations with outer DECLARE
• Added comprehensive test coverage for various DECLARE scenarios (mixed case, inside BEGIN...END blocks, inside EXECUTE IMMEDIATE, after comments, in arrays)
• Updated README and Copilot instructions to document this limitation of automated assignment

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
index.js	Implemented hasOuterDeclare() function and integrated DECLARE detection into reservation assignment logic
test/index.test.js	Added 5 test cases covering DECLARE detection in various scenarios
README.md	Added "Limitations of Automated Assignment" section documenting DECLARE restriction
.github/copilot-instructions.md	Added section 5 documenting outer DECLARE detection logic

Comments suppressed due to low confidence (1)

index.js:204

• The DECLARE detection doesn't handle cases where queries is passed as a function that returns SQL with an outer DECLARE statement. The check on line 191 only evaluates the function object itself (which will stringify to something like "function (ctx) { ... }"), not the SQL it returns.

When the function is executed later (lines 196-204), the result could contain an outer DECLARE, which would cause a syntax error since the reservation SET statement would be prepended before it. Consider either checking the function's return value at execution time, or documenting this as a known limitation requiring manual assignment.

        // Check for outer DECLARE before wrapping
        if (hasOuterDeclare(queries)) {
          return originalQueriesFn.apply(this, [queries])
        }

        if (typeof queries === 'function') {
          queriesArray = (ctx) => {
            const result = queries(ctx)
            if (typeof result === 'string') {
              return [statement, result]
            } else if (Array.isArray(result)) {
              return [statement, ...result]
            }
            return result
          }