Document JumpProcesses public API

[ChrisRackauckas-Claude]

This draft PR should be ignored until reviewed by @ChrisRackauckas.

Summary

• Adds SciMLStyle-style source docstrings for JumpProcesses-owned public/exported API gaps around pure leaping, RSSA bracketing, aggregator helper predicates, tau-leaping algorithms, variable-rate function-wrapper aggregation, and spatial topology/mass-action APIs.
• Expands docs/src/api.md so the owned public API is rendered through @docs blocks instead of leaving exported names out of the manual.
• Adds a focused QA test that checks the curated JumpProcesses-owned public API has both source docstrings and rendered API entries.
• Preserves the existing source layout; unrelated whole-file formatter changes were removed.

Validation

• git diff --check upstream/master...HEAD
• Post-rebase GROUP=QA Pkg.test() passed: QA Tests 14/14.
• Full curated GROUP=All Pkg.test() passed locally on the cleaned patch.
• docs/make.jl passed locally with the checkout developed into the docs environment. Documenter reported the existing missing-docstring and large-example warnings, then rendered HTML successfully.