pgproto

Summarize the changes

• feat: support result format for pg_descripe

• feat: implement a simplifed version of OTM query_span

• feat: extend query constructors and fix typo

• feat: make plan optimization a public method

Ensure that

• New code is covered by unit and integration tests.
• Related issues would be automatically closed with gitlab's closing pattern (Closes #1, #2).
• Public modules are documented (check the rendered version with cargo doc --open).
• (if PEST grammar is changed) EBNF grammar reflects these changes (check the result with railroad diagram generator.

Next steps

• Update sbroad submodule in picodata/picodata.
• (if EBNF grammar is changed) create a follow-up issue in picodata/docs.