Improve trend prediction behavior

[nimish]

Summary

• simplify the nonlinear trend API to a single monotone decreasing mode across the estimator and example tooling
• fix trend prediction on shorter windows by slicing the fitted trend vector to the requested period count
• document and test that predict() still requires a regular timestamp grid without gaps

Test plan

• uv run --project /Users/nimish/Projects/bennet/estimator/.worktrees/tsgam-trend-improvement --directory /Users/nimish/Projects/bennet/estimator/.worktrees/tsgam-trend-improvement pytest test/test_tsgam_trend.py test/test_tsgam_multi_frequency.py -q

Made with Cursor

[github-actions]

Test Results

149 tests  +5   149 ✅ +5   51s ⏱️ -1s
  1 suites ±0     0 💤 ±0 
  1 files   ±0     0 ❌ ±0 

Results for commit cd25b55. ± Comparison against base commit 411b541.

This pull request removes 3 and adds 8 tests. Note that renamed tests count towards both.

test.test_tsgam_trend ‑ test_explicit_nonlinear_decreasing_is_nonincreasing
test.test_tsgam_trend ‑ test_explicit_nonlinear_increasing_is_nondecreasing
test.test_tsgam_trend ‑ test_legacy_nonlinear_alias_remains_nonincreasing

test.test_tsgam_trend ‑ test_predict_beyond_training[linear]
test.test_tsgam_trend ‑ test_predict_beyond_training[nonlinear]
test.test_tsgam_trend ‑ test_predict_full_range[linear]
test.test_tsgam_trend ‑ test_predict_full_range[nonlinear]
test.test_tsgam_trend ‑ test_predict_gapped_subset[linear]
test.test_tsgam_trend ‑ test_predict_gapped_subset[nonlinear]
test.test_tsgam_trend ‑ test_predict_subset_before_end[linear]
test.test_tsgam_trend ‑ test_predict_subset_before_end[nonlinear]

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
src/tsgam_estimator
tsgam_estimator.py					1740-1741, 1856, 1924
Project Total

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