Add picker session management

[lambdalisue]

Summary

• Add session management functionality to save and resume picker states
• Implement FallSession and FallResume commands for managing sessions
• Store picker context including query, selection, items, and UI state

Features

New Commands

• :FallSession - Opens a picker to browse and resume saved sessions
• :FallResume [filter] - Resume a specific session by name or index
  • Resume latest session: :FallResume
  • Resume by name: :FallResume file
  • Resume by index: :FallResume file#2

Session Management

• Sessions are automatically saved when closing a picker (except for internal pickers like @action and @session)
• Sessions store the complete picker state:
  • Query text
  • Selected items
  • Collected and filtered items
  • Cursor position and scroll offset
  • Active matcher, sorter, renderer, and previewer indices

Session Picker

• Browse all saved sessions with :FallSession
• Preview shows session details including source, query, and filtered items
• Dedicated renderer shows session number, name, and arguments

Implementation Details

Core Components

• session.ts: Manages session storage with compression and a 50-session limit
• PickerContext: Captures and restores internal picker state
• UniqueOrderedList: Maintains insertion order while ensuring uniqueness
• Refactored setup/teardown logic into fall#internal#picker module

Extensions

• Source: session.ts - Provides session items for the session picker
• Renderer: session.ts - Formats session display
• Previewer: session.ts - Shows detailed session information
• Action: session.ts - Implements resume action with timer to avoid nesting

Test plan

• Basic session saving when closing pickers
• Resume sessions with :FallResume
• Browse sessions with :FallSession
• Resume specific sessions by name and index
• Session preview shows correct information
• Old sessions are pruned when limit is exceeded
• Internal pickers (@action, @session) don't create sessions

🤖 Generated with Claude Code

[codecov]

Codecov Report

Attention: Patch coverage is 87.35632% with 22 lines in your changes missing coverage. Please review.

Project coverage is 82.09%. Comparing base (c2fa4f8) to head (f9e0964).
Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
denops/fall/processor/match.ts	52.38%	10 Missing ⚠️
denops/fall/processor/preview.ts	69.23%	4 Missing ⚠️
denops/fall/processor/render.ts	73.33%	4 Missing ⚠️
denops/fall/processor/sort.ts	71.42%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #36      +/-   ##
==========================================
+ Coverage   81.14%   82.09%   +0.94%     
==========================================
  Files          24       26       +2     
  Lines        1671     1793     +122     
  Branches      161      178      +17     
==========================================
+ Hits         1356     1472     +116     
- Misses        312      318       +6     
  Partials        3        3              

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