feat: Adds span labeling pipeline with prompt references, exponential magnitude slider, and 10 jsPsych plugins

[aaronstevenwhite]

Description

Adds a complete span labeling pipeline from data model through deployment, 10 new jsPsych plugins, prompt span references ([[label]] syntax), an exponential magnitude estimation slider, and an interactive gallery with 17+ demos.

Motivation

The experiment framework needed token-level annotation (span labeling), additional task types beyond the initial rating/forced-choice plugins, and a way for prompts to reference highlighted spans with matching colors. Magnitude estimation also needed a better input method than a plain number field.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (no functional changes)
• Tests (adding or updating tests)

Checklist

• I have read the CONTRIBUTING guidelines
• My code follows the project's style guidelines
• I have run uv run ruff check . and uv run ruff format .
• I have run uv run pyright with no errors
• I have added tests that prove my fix/feature works
• All tests pass (uv run pytest tests/)
• I have updated documentation as needed

Testing

Python (79 span + 13 prompt reference tests):

• uv run pytest tests/deployment/jspsych/test_trials.py -- prompt span reference parsing, color assignment, resolver, integration
• uv run pytest tests/items/test_spans.py -- span data model, composability, validation
• uv run pytest tests/tokenization/ -- tokenizer backends

TypeScript (83 tests, 0 type errors, 0 Biome errors):

• pnpm run test -- plugin info/instantiation (rating, forced-choice, span-label, cloze, magnitude), exponential slider math (8 tests), span-renderer (22 tests), randomizer, list-distributor
• pnpm run typecheck -- strict mode with exactOptionalPropertyTypes, noUncheckedIndexedAccess
• pnpm run check -- Biome lint + format clean

Key features to verify manually:

• Exponential magnitude slider: drag, click, arrow keys, value display, reference tick at 1/3
• Prompt span references: [[label]] resolves to highlighted HTML with matching stimulus colors
• Multi-select demo: 3 options (no redundant "Both")
• Gallery demos: all 17+ demos render correctly with tabbed Demo/Python/Trial JSON views

Screenshots (if applicable)

N/A -- interactive demos viewable via uv run mkdocs serve