fix: resolve visualization helper regressions

[stefan-jansen]

Summary

• fix plot_rolling_sharpe so externally supplied rolling results drive the rendered window set
• keep rolling Sharpe reference labels readable on narrow layouts and fail loudly on unmatched windows
• use adaptive cost-waterfall label formatting so small costs no longer round to hBc0 (0.0%)
• add regression coverage for both visualization helpers
• bump release to 0.1.0b21

Validation

• uv run pytest tests/test_visualization/test_portfolio_plots.py -q
• uv run pytest tests/test_visualization/test_backtest.py -q -k 'cost_waterfall'
• uv run ruff check src tests
• uv run ruff format --check src tests
• uv run ty check
• uv run --extra docs mkdocs build --strict
• uv build
• uv run pytest tests/ -q

Full suite result: 5226 passed, 21 skipped

[Copilot]

Pull request overview

Fixes two visualization helper regressions: plot_rolling_sharpe now honors externally supplied rolling result windows and fails loudly when no series match, with reference labels repositioned to fit narrow layouts. plot_cost_waterfall uses adaptive currency/percent formatting so small costs render with appropriate precision. Adds regression tests and bumps version to 0.1.0b21.

Changes:

• plot_rolling_sharpe: derive windows from rolling_result.sharpe.keys() when not specified; raise ValueError if no series match; move reference annotations to top right with right margin.
• New _formatting.py helpers (format_currency_adaptive, format_percent_adaptive) used in plot_cost_waterfall.
• Regression tests + CHANGELOG/version bump.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/ml4t/diagnostic/visualization/portfolio/risk_plots.py	Fix window selection and annotation positioning for plot_rolling_sharpe.
src/ml4t/diagnostic/visualization/backtest/cost_attribution.py	Use adaptive formatters for waterfall labels.
src/ml4t/diagnostic/visualization/backtest/_formatting.py	New shared adaptive currency/percent formatters.
tests/test_visualization/test_portfolio_plots.py	New regression tests for rolling Sharpe behavior.
tests/test_visualization/test_backtest.py	New regression test for small-cost waterfall labels.
src/ml4t/diagnostic/init.py	Bump version to 0.1.0b21.
CHANGELOG.md	Document fixes under 0.1.0b21.

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