feat(schema): ignore listed statements and locate rejected ones

[omer-cengel]

Summary

Migration histories contain many statements that never change a table's columns, types, or nullability, such as indexes, grants, functions, triggers, comments, and seed data. Schema sources now accept a documented list of these statements and leave the schema model unchanged, so an existing migration directory loads without edits. Every other statement is still rejected, and the diagnostic now names the line the statement begins on.

Changes

• Accept and ignore CREATE/ALTER/DROP INDEX, COMMENT ON TABLE/COLUMN/VIEW, CREATE EXTENSION, CREATE/ALTER/DROP SEQUENCE, GRANT, REVOKE, CREATE [OR REPLACE] FUNCTION with an untagged $$ ... $$ body, DROP FUNCTION, CREATE/DROP TRIGGER, INSERT, UPDATE, DELETE, and CREATE TYPE ... AS ENUM. Ignored statements are not resolved against the schema.
• Accept and ignore the ALTER TABLE constraint actions: ADD [CONSTRAINT name] PRIMARY KEY, UNIQUE, or FOREIGN KEY, ADD CONSTRAINT name CHECK, DROP CONSTRAINT [IF EXISTS], and RENAME CONSTRAINT. They may stand alone or beside modeled actions. The altered table must still exist.
• Reject a CREATE FUNCTION whose own body is not dollar-quoted at the line it begins on, even when the parser captures a later dollar-quoted function into it.
• Report every other statement as Unsupported schema statement: <kind> at line <n>. The line is derived from the parser's token chain, so comments and multi-line function bodies do not shift it. The compiler prefixes the message with the failing migration file.
• Document the ignored list, the parser limitations (untagged $$ only, with tagged delimiters such as $body$ being a syntax error; COMMENT ON limited to TABLE, COLUMN, and VIEW; unnamed ADD CHECK being a syntax error), and the new diagnostic.

Scope and non-goals

• Ignored statements and constraint actions are not modeled; constraints an ALTER TABLE adds are not recorded.
• SQL is not split or pre-processed to work around parser limitations, so tagged dollar quotes and other COMMENT ON targets remain syntax errors.
• Other ALTER TABLE actions such as SET DEFAULT, other DROP objects such as views, ALTER TYPE, and every other statement kind remain rejected. Missing-reference and syntax diagnostics are unchanged.