fix: capture metadata for explicit query name (based on filename)

feat: experiment support for -- @Markers

Allows to instrument the queries for further testing with regresql (primarily).

Example:

```sql`
-- name: insert-order
INSERT INTO orders (user_id, total) VALUES (:user_id, :total);

-- @verify
SELECT * FROM orders WHERE user_id = :user_id;
```sql`

Which defines the verification query. @marker query is access using

```go
if q.HasSection("verify") {
  verifyQuery := q.SectionQuery("verify")
}
```

feat: added support for @param in sqlc style

fix: skip comments before name directive

scanner now properly skips comment lines and empty lines before
the -- name: directive

feat: include better support for positional parameter notation ()

feat: added support for query.Path and query.Args

- Path identifies the source file

feat: store's Queries and QueryNames

Exposed raw queries (for use with sql.NamedArg)