Refactor budget enforcement to use exception-based control flow

[rbharvs]

Summary

• Replace manual budget checking with BudgetExceeded exception-based control flow
• Centralize budget logic in OutputBudget.debit() method for atomic operations
• Remove budget parameter from StreamingRegexSearcher - budget now handled at Grepper level
• Update Globber to debit budget by path length instead of count for more accurate resource tracking

Benefits

• Eliminates race conditions between budget checking and debiting
• Cleaner separation of concerns - budget enforcement centralized in one place
• More maintainable code with less repetitive manual budget checks
• Consistent error handling across all components using BudgetExceeded exceptions

Changes

• Updated StreamingFileReader, Globber, and Grepper to use exception-based budget handling
• Removed obsolete budget-related tests from StreamingRegexSearcher (budget now handled upstream)
• Fixed all test method signatures and removed unused budget parameters
• Updated protocol interface to reflect new budget handling architecture

Test plan

• All existing tests pass (145/145)
• Code quality checks pass (ruff, mypy)
• Budget enforcement still works correctly at component boundaries
• Exception handling properly sets truncation flags