Add missing string_related/suffix_tree/string_function_calculation port #1

The clojure↔python snippet audit paired all scripts by identical src/
relative path: 393 pairs match, except one clojure-only script with no
python twin:

• src/string_related/suffix_tree/string_function_calculation.clj
  (python has no suffix_tree/ directory at all)

This benchmark is also a top-slowest workload (JVM #3 / clojure-rs #6 by
callgrind_instructions), so the missing port blocks the cross-runtime
comparison there.

Acceptance

• Add src/string_related/suffix_tree/string_function_calculation.py
  implementing the same algorithm with the same time/space complexity as
  the .clj (audit the .clj body first; match its approach, not just
  its outputs).
• Add shared test cases under the standard resources layout
  (<area>/<problem>/<stem>/test_case_N/{input,output}.txt).
• run_tests.py green on the new cases; benchmark appears in the next
  perf-callgrind sweep with 0 failures.

AI-Tool: Muse Code (Meta Muse Spark)