Massive Optional + Functions update

[1NepuNep1]

• Added almost all functions except ones working with containers
• Supported Options typedef
• CAST, LEAST (MIN_OF), GREATEST are covered like in PostgreSQL

[Copilot]

Pull Request Overview

This PR adds comprehensive YDB function support and improvements to optional type handling. The update expands from a basic set of functions to nearly complete YDB function coverage including mathematical, string processing, datetime, and regular expression functions.

• Adds extensive function library covering mathematical operations, string processing, datetime manipulation, regular expressions, and specialized YDB functions
• Implements proper Optional typedef support with syntax handling for both Optional<type> and type? notations
• Replaces the recursive function call AST node with standard function expression nodes for better compatibility
• Enhances type system with nullable type detection and proper Optional type extraction

Reviewed Changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
internal/sql/astutils/walk.go	Removes RecursiveFuncCall node handling from AST walker
internal/sql/astutils/rewrite.go	Removes RecursiveFuncCall node handling from AST rewriter
internal/sql/ast/recursive_func_call.go	Deletes the entire RecursiveFuncCall AST node definition
internal/engine/ydb/stdlib.go	Adds window and C++ function libraries to default schema
internal/engine/ydb/lib/window.go	Implements comprehensive window function support
internal/engine/ydb/lib/cpp/*.go	Adds extensive C++ function libraries for specialized operations
internal/engine/ydb/lib/cpp.go	Aggregates all C++ function libraries
internal/engine/ydb/lib/basic.go	Expands basic functions with proper type handling
internal/engine/ydb/lib/aggregate.go	Refactors aggregate functions with improved organization
internal/engine/ydb/convert.go	Enhances parser with Optional type support and CAST expressions
internal/codegen/golang/ydb_type.go	Adds Optional type extraction and nullable type detection
internal/codegen/golang/query.go	Updates parameter mapping to handle Optional types

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[kprokopenko]

Этот комментарий лучше перенести в описание метода extractBaseType