Improved OCEL Import and Memory Usage + Misc Bug Fixes

[aarkue]

This PR makes multiple bundled changes, mainly improving OCEL import and export, memory improvements for the SlimLinkedOCEL, plus some new analysis (bindings) functions.

• New ReadableOCEL and AppendableOCEL traits; OCEL exporters (CSV, XML, SQL, JSON) and the JSON importer are generic over them
• SlimLinkedOCEL implements AppendableOCEL, with auto-declare types, auto-grow attributes, and value coercion via new OCELAttributeValue::try_coerce_to; misordered streams are buffered and resolved on finalize
• import_ocel_json_into and import_ocel_xml_into stream JSON / XML directly into any AppendableOCEL (e.g., SlimLinkedOCEL) without materializing an OCEL first; SlimLinkedOCEL::import_from_* uses the streaming paths automatically
• ReadableOCEL::iter_events_of_type / iter_objects_of_type (default filters; SlimLinkedOCEL overrides via per-type indices, avoiding a full scan per type in SQL export)
• New OCELAttributeType::as_type_str returns &'static str (cheaper than to_type_string)
• EventIndex / ObjectIndex are now u32-backed; into_inner returns u32 (Breaking)
• SlimLinkedOCEL, SlimOCELEvent, SlimOCELObject no longer derive Deserialize (still serialize); construct via Importable or AppendableOCEL (Breaking)
• SlimOCELEvent::relationships and SlimOCELObject::relationships are now Vec<(QualifierIdx, ObjectIndex)> (was Vec<(String, ObjectIndex)>); resolve qualifier strings via SlimLinkedOCEL::qualifier_str (Breaking)
• CSV exporter streams rows instead of buffering all rows; tracks (time, object_id) pairs in a HashSet to skip redundant object-attribute rows
• SlimLinkedOCEL::from_ocel now goes through AppendableOCEL, so it shares attribute coercion, schema-grow, and duplicate-id detection with the streaming import paths. Behavior changes: events/objects with attribute names not in the declared type schema grow the schema (before they were silently dropped); duplicate event/object ids are skipped with a warning (before they were kept but unreachable); references to undeclared types auto-create the type (before they were dropped with warning)
• try_json_to_ocel returning Result<OCEL, serde_json::Error> added alongside the existing panicking json_to_ocel
• SlimLinkedOCEL::get_o2o_rev_obs_of_obtype / get_e2o_rev_evs_of_evtype: qualifier-optional reverse-relation getters filtered by type
• New public object-centric analysis functions (also exposed as bindings): per-event sojourn and synchronization times with optional top_k (analysis::object_centric::oc_performance), E2O (event_type, object_type) counts and source -> target conversion rate (analysis::object_centric::oc_statistics), and per-object-type directly-follows graph and activity-trace variants (discovery::object_centric::dfg / variants)
• Fix SQL export/import of floats and timestamps: floats are written as DOUBLE PRECISION (full f64 precision) and timestamps as naive UTC (avoids a double-applied timezone offset); import maps DOUBLE / DOUBLE PRECISION columns back to float, so round-trips no longer drop float attributes
• New direct dependency on hashbrown for the slim per-id hash tables

[cpitsch]

Looks good 👍 just some small questions :)

[cpitsch]

👍