chore: remove all VectorBT references — raptorbt stands on its own

- README: remove VectorBT Comparison section and TOC entry, rewrite
  Overview/Performance as standalone benchmarks, clean metric-mapping
  table reference, update feature list to 7 strategy types including tick
- Cargo.toml / pyproject.toml: rewrite description without VectorBT mention
- __init__.py: rewrite module docstring without comparative framing
- Rust comments (engine.rs, position.rs, signals/processor.rs, core/types.rs,
  python/bindings.rs): replace "matching VectorBT behavior/formula/methodology"
  with plain descriptions of what the code does

Co-Authored-By: porcelaincode <contact@alphabench.in>

src/portfolio/position.rs

@@ -112,7 +112,7 @@ impl PositionManager {
         let pos = &self.position;
         let multiplier = pos.direction.multiplier();
 
-        // Calculate P&L (matching VectorBT: gross - entry_fees - exit_fees)
+        // Calculate P&L: gross - entry_fees - exit_fees
         let gross_pnl = (exit_price - pos.entry_price) * pos.size * multiplier;
         let total_fees = pos.entry_fees + exit_fees;
         let pnl = gross_pnl - total_fees;