Implement max block for token scope - #23

…icipation

This implements the missing <max> block feature that was requested in the README.
Unlike <isolate>, the <max> block participates in global priority calculation
while still enforcing a local token limit.

Key features:
- Specify a token limit for a section of the prompt with tokenLimit prop
- Inner scopes participate in global priority calculation (unlike isolate)
- Uses binary search to find optimal priority cutoff within token limit
- Includes comprehensive test cases demonstrating the functionality
- Full integration with existing priompt rendering pipeline

Usage:
<max tokenLimit={100}>
  <scope p={200}>High priority content</scope>
  <scope p={100}>Lower priority content</scope>
</max>

The content with p={200} will be prioritized globally, but the max block
will ensure total tokens don't exceed 100.