fix: re-implement trim

Summarize the changes

• fix: re-implement trim

Previous implementation treated TRIM as an SQL built-in function, but in reality it is a special expression in SQL that differs from functions. The main problem is as that TRIM is not a name, it can't be wrapped with double quotes. Moreover, if we treat it as a function, we need some special hacks to modify is arguments. Now, these problems solved in a custom parsing logic.

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.