perf: add and harden synthetic scale-test suite

[Arths17]

Summary

• add a synthetic performance stress-test suite under tests/perf/scale_test
• include generator-driven modules with dense typing, inheritance chains, and import mesh patterns
• improve generated service transact typing with explicit callable-fallback wrapper usage and value narrowing
• make tests/README.md portable for public contributors (cross-platform Python invocation guidance)
• remove tracked __pycache__ bytecode artifacts from the stress-test package

Validation

• python3 test.py --no-test --no-conformance --no-jsonschema
• python -m py_compile tests/perf/scale_test/generate_stress_test.py
• additional local lint/format passes during iteration (ruff, flake8, autopep8)

Notes

• this change targets stress/perf coverage and docs ergonomics, not runtime feature behavior

[Copilot]

Pull request overview

Adds a synthetic, generator-driven Python “scale test” workload under tests/perf/scale_test to stress Pyrefly indexing/type-solving performance, plus contributor-facing documentation for running/regenerating the suite.

Changes:

• Introduces a deterministic generator script to produce a dense import mesh, deep inheritance chains, and heavily-typed service/protocol APIs.
• Checks in the baseline (“core-only”) generated modules for immediate use.
• Adds tests/README.md describing the perf suite structure and cross-platform invocation guidance.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
tests/README.md	Documents the synthetic perf suite, how to run the generator, and expected outputs.
tests/perf/scale_test/generate_stress_test.py	Generator for producing the synthetic module graph and baseline core modules.
tests/perf/scale_test/init.py	Package initializer exporting the baseline core modules.
tests/perf/scale_test/base_types.py	Checked-in generated core module used as baseline perf workload input.
tests/perf/scale_test/data_layer.py	Checked-in generated core module used as baseline perf workload input.
tests/perf/scale_test/service_mesh.py	Checked-in generated core module used as baseline perf workload input.
tests/perf/scale_test/domain_models.py	Checked-in generated core module used as baseline perf workload input.
tests/perf/scale_test/orchestration.py	Checked-in generated core module used as baseline perf workload input.

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[Arths17]

For the reviewer: Although the line count is large (+13k), 99% of this PR consists of generated Python modules under tests/perf/scale_test/.

I recommend focusing your review on:

1. generate_stress_test.py: This is the logic that drives the suite.
2. tests/README.md: The documentation for how to use this suite.
3. base_types.py: A representative sample of what the generated code looks like (typing density, circular imports, etc.).

Everything else is synthetic data for benchmarking the indexing engine.