feat: add analysis and visualization modules ported from TypeScript

Port 6 analysis functions from TS analysis.ts (pitch_times,
condensed_durations, durations_of_pitch_onsets, segment_by_duration,
pattern_counter, chroma_seq_to_condensed_pitch_nums) and add 3
matplotlib visualization functions (plot_melodic_contour,
plot_pitch_prevalence, plot_pitch_patterns) mirroring the IDTAP
web app's D3.js-based analysis views.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jon-myers