fpstreams 2.4.1

fpstreams 2.4.1 reorganizes the query planner and execution internals while preserving the public API and pipeline behavior. Existing 2.4.0 code needs no migration.

• Separate relational candidate recognition and tree compilation from unary-stage compilation and plan caches.
• Move native grouping and Collector grouping into dedicated modules. Dispatch still checks the live source, selectors, and Collector callbacks.
• Extract numeric, frequency, and materialization helpers from synchronous terminals, keeping source ownership, cleanup, and fallback rules.
• Add regression coverage for compiler and source-opener replacements, and update the timer-based grouping check to target the extracted execution loop.

Validation includes the full Python suite, three input sizes in the engine matrix, paired performance and allocation checks, and clean wheel installs on Python 3.11 through 3.14.