Remove redundant GIL handoff in VM dispatch

[proboscis]

Summary

• share one materialized dispatch effect object across type-filter checks and handler expression construction
• remove py: Python from Kleisli::{apply, apply_with_run_token} and IRStreamProgram::start, while pushing Python attachment into Python-backed implementations
• drop RustKleisliStream GIL wrappers and add/update regression tests for the new call signatures and dispatch object reuse

Validation

• cargo test --manifest-path packages/doeff-vm-core/Cargo.toml
• PYTHONHOME=/home/kento/.local/share/uv/python/cpython-3.14.0b1+freethreaded-linux-x86_64-gnu PYO3_PYTHON=/home/kento/.orch/worktrees/vm-perf-gil-cleanup/5c5ab6_codex_20260314-164318/.venv/bin/python LD_LIBRARY_PATH=/home/kento/.local/share/uv/python/cpython-3.14.0b1+freethreaded-linux-x86_64-gnu/lib cargo test --manifest-path packages/doeff-vm/Cargo.toml
• uv run pytest packages/doeff-vm-core/tests/test_gil_cleanup_architecture.py
• uv run pytest tests/ -> 1193 passed, 12 skipped
• uv tool run semgrep --config .semgrep.yaml packages/doeff-vm-core/src/vm/step.rs packages/doeff-vm-core/src/kleisli.rs packages/doeff-vm-core/src/handler.rs packages/doeff-vm-core/src/vm/dispatch.rs packages/doeff-vm-core/src/vm/vm_trace.rs -> 0 findings

Acceptance Criteria

• Kleisli::apply / apply_with_run_token no longer take py: packages/doeff-vm-core/src/kleisli.rs, packages/doeff-vm-core/src/handler.rs
• IRStreamProgram::start no longer takes py: packages/doeff-vm-core/src/handler.rs, packages/doeff-core-effects/src/handlers/mod.rs, packages/doeff-core-effects/src/scheduler/mod.rs
• RustKleisliStream::resume/throw no longer wrap Python::attach: packages/doeff-vm-core/src/kleisli.rs
• dispatch_to_pyobject is materialized once and passed into handler expansion through ensure_dispatch_effect_object(...): packages/doeff-vm-core/src/vm/dispatch.rs, packages/doeff-vm-core/src/vm/vm_trace.rs
• no production behavior regression observed: full Python suite passed after rebuild

Notes

• cargo test --manifest-path packages/doeff-core-effects/Cargo.toml already fails on origin/main at baseline commit 9aa8f77c because the crate test target aliases DispatchEffect = Effect, which diverges from the doeff-vm-core trait signature. This PR does not introduce that failure.
• Ref: vm-perf-gil-cleanup