Add prime-or-square-or-semiprime-window procedural heuristic and metadata

[GISMO-1]

Motivation

• Reduce expanded-case churn by combining the existing prime/square fast-path with an SPF-gated semiprime escalation so non-prime/non-square candidates that look semiprime can take the semiprime action.
• Provide richer diagnostics for exported expanded-case metadata to record which gating stage applied and SPF diagnostics for post-hoc analysis.

Description

• Add a new procedural heuristic prime-or-square-or-semiprime-window in src/strausforge/identities.py that preserves prime-or-square-window behavior for primes/squares and otherwise applies semiprime gating (bounded SPF) to choose the semiprime action (128 initial window) or default (8).
• Register the new option in PROC_HEURISTIC_CHOICES and update CLI help/error strings in src/strausforge/cli.py so all relevant commands accept and document the new heuristic.
• Use semiprime_window_trigger in src/strausforge/hardness_core.py when emitting expanded-case metadata and add proc_stage (one of "prime"|"square"|"semiprime"|"none"), semiprime_triggered (bool), and spf_bound_used (int) to exported records.
• Add tests in tests/test_identities_verify.py and update tests/test_factor_meta.py to exercise combined-heuristic parity with POSW on prime/square inputs and semiprime triggering behavior, and to assert the new proc_stage field is present.

Testing

• Installed dev deps with python -m pip install -e '.[dev]' and ran linting with ruff to validate formatting and imports, which passed after formatting fixes.
• Ran targeted tests pytest -q tests/test_identities_verify.py tests/test_factor_meta.py tests/test_cli.py and the full suite pytest -q, with all tests passing (final run: 77 passed, 1 skipped).
• Performed the acceptance-style check by calling run_hardness over 22_000_000–23_000_000 with proc_heuristic='prime-or-square-window' and proc_heuristic='prime-or-square-or-semiprime-window'; the results were: POSW expanded = 10, combined expanded = 0, and combined expanded_primes = 0.

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Codex Task