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>

pyproject.toml

@@ -5,7 +5,7 @@ build-backend = "maturin"
 [project]
 name = "raptorbt"
 version = "0.4.0"
-description = "High-performance Rust backtesting engine with Python bindings. Drop-in VectorBT replacement with up insanely faster performance at fractional memory footprint."
+description = "High-performance Rust backtesting engine with Python bindings. Bar-level and tick-level simulation with sub-millisecond execution and a minimal footprint."
 readme = "README.md"
 requires-python = ">=3.10"
 license = {file = "LICENSE"}