Refactor bin/release.rb: structure the release script

[d3mlabs-ai-flow]

From review discussion on #133 (thread): bin/release.rb has grown into a ~250-line procedural script of top-level methods and constants, and #133 added more (two lockstep formulas via FORMULA_PATHS, per-formula url+sha surgery). It deserves a proper refactor rather than more accretion.

Candidate shape:

• Extract cohesive steps (version bump, tag/push, GitHub release, formula update) into small objects or a class per concern, following the repo's typed, constructor-injected conventions where the polyglot ruby -x bootstrap allows.
• Typed errors instead of bare abort strings; tests for the pure parts (version parsing/increment, formula substitution) using real files in temp dirs.
• Consider whether this converges with Absorb per-repo release scripts: builtin dev release with pluggable publishers #70 (builtin dev release with pluggable publishers) — if that lands, this script may be absorbed rather than refactored in place.

Out of scope for #133 per review; tracked here.