v0.4.1: Fix fractional volume truncation in OHLC and Spot ticks

[mwlang]

Summary

• Bug fix: base_volume and target_volume were coerced with .to_i in both Quant::Ticks::OHLC and Quant::Ticks::Spot, silently truncating fractional values. Changed to .to_f — crypto and many futures markets routinely express fractional volumes (e.g. 0.12345 BTC).
• Regression specs: Added test blocks that assert both the value and the class (be_a(Float)) for fractional crypto-style volumes so future regressions fail loudly rather than being masked by Ruby's == coercion between Integer and Float.
• Gemspec: Fixed changelog_uri to point directly to CHANGELOG.md in the repo.
• Gitignore: Added .serena/ to .gitignore.

Test plan

• bundle exec rspec spec/lib/quant/ticks/ohlc_spec.rb passes, including new fractional-volume context
• bundle exec rspec spec/lib/quant/ticks/spot_spec.rb passes, including new fractional-volume context
• bundle exec rspec full suite passes

Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.15%. Comparing base (01bdb79) to head (1ce71c3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main       #9   +/-   ##
=======================================
  Coverage   99.15%   99.15%           
=======================================
  Files          75       75           
  Lines        2243     2243           
=======================================
  Hits         2224     2224           
  Misses         19       19           

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