* feat: add __schema__ tag for promql parser
* feat: disable matcher op other than equals
* test: add more test to ensure context getting reset
* test: add integration test
* test: refactor tests
* refactor: remove duplicated test code
* refactor: update according to review comments
* test: add sqlness test for cross schema scenario
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Co-authored-by: Ruihang Xia <waynestxia@gmail.com>