Align Split Miner gateway handling and SM2 lifecycle behavior with the reference implementation

[cRennert]

This PR revises the Split Miner implementation to better match the reference miner behavior across filtering, split discovery, join discovery, OR handling, lifecycle-aware SM2 logs, and BPMN reduction.

Key changes include:

• Replace the previous split/join handling with an Oracle-style split discovery and RPST/SESE-based join discovery.
• Add lifecycle-aware SM2 parsing with overlap-based concurrency detection for complex logs.
• Pin SM2 filtering to the reference eta = 1.0 behavior and make SM2 OR handling mandatory.
• Add gateway-map based inclusive-join handling, OR-split promotion, compact self-loop export, and optional BPMN gateway collapsing.
• Update Split Miner smoke/regression tests to reflect the new reference-aligned behavior.

[fit-alessandro-berti]

Dear @cRennert

Thanks for the contribution.

Can you double check on the following comments?

Possible Revisions Before Merge

• Restore or replace coverage for the removed SM2 improper-completion regression. The previous test asserted that A can repeat through a D-free loop in the paper-style example; this branch no longer satisfies that property. If the behavior change is intentional, document it explicitly in the PR and changelog.
• Consider compatibility shims for removed modules such as pm4py.algo.discovery.split_miner.heuristics, concurrency.refined, dfg_discovery.refined, and joins.classic, or call out the breaking import changes clearly.
• Add focused unit tests for gateway_map.py and rpst_tree.py, especially loop joins, fake entry/exit flows, token generator placement, and non-biconnected graphs.
• Add an explicit regression test showing that SM2 ignores user-provided eta and minimize_or_joins by design, so future reviewers do not mistake this for an accidental parameter bug.
• Include a short rationale or reference comparison for the large changes to classic filtering, split discovery, and join discovery, because the expected gateway counts changed from the prior tests.