Add optional Python bindings via PyO3 + maturin

[muk2]

Summary

Implements an optional Python interoperability layer for pgrsql using PyO3 and maturin, enabling SQL parsing, optimization, and analysis from Python.

• Feature-gated: Python bindings compile only with --features python, keeping the core Rust crate unaffected
• PyO3 bindings (src/python.rs): 5 Python-callable functions exposing the Rust SQL engine
• maturin packaging (pyproject.toml): Build wheels for macOS, Linux, and Windows with maturin build --release
• Python package (python/pgrsql/__init__.py): Clean import pgrsql interface with re-exports
• Library crate (src/lib.rs): Exposes all modules publicly for external consumption

Python API

import pgrsql

# Parse SQL statements to normalized form
statements = pgrsql.parse_sql("SELECT * FROM users WHERE age > 18")

# Format and optimize a single SQL statement
formatted = pgrsql.format_sql("select id,name from users where age>18")

# Analyze query structure (returns dict with feature flags)
analysis = pgrsql.analyze_query("SELECT * FROM a JOIN b ON a.id = b.id")
# {'has_select': True, 'has_joins': True, 'join_count': 1, ...}

# Parse PostgreSQL EXPLAIN output
plan = pgrsql.parse_explain("Seq Scan on users (cost=0.00..35.50 rows=100)")

# Check if a query is an EXPLAIN query
pgrsql.is_explain_query("EXPLAIN SELECT 1")  # True

Building

# Local development
maturin develop

# Release wheel
maturin build --release

# Standard Rust build (no Python)
cargo build

# Build with Python feature
cargo build --features python

Files Changed

File	Description
src/python.rs	PyO3 module with 5 functions + 6 unit tests
src/lib.rs	New library crate entry point
src/main.rs	Updated imports to use pgrsql:: paths
Cargo.toml	Added pyo3 optional dep, [features], [lib] section
pyproject.toml	maturin build configuration
python/pgrsql/__init__.py	Python package with re-exports

Test plan

• cargo build passes
• cargo test — all 225 tests pass
• Python module compiles with feature flag
• maturin develop builds wheel and import pgrsql works
• Verify on Python 3.9+

Closes #45

🤖 Generated with Claude Code