Add behavior table merging functionality for JABS-postprocess

[bergsalex]

This is the code implementation half of KLAUS-118.

Implements behavior table merging functionality to address requirements in YODA-118 and YODA-65. This enables aggregation of bout tables per-behavior with header preservation, supporting both bout and bin table types through new CLI commands.

New functions:

• merge_behavior_tables() - Merges multiple behavior tables of the same type and behavior
• merge_multiple_behavior_tables() - Merges multiple sets of behavior tables grouped by behavior

These are exposed through new CLI commands:

• merge-tables - Merge specific behavior table files of the same type
• merge-multiple-tables - Auto-group and merge tables from a folder by behavior

Example CLI usage:

  # Merge specific tables of the same behavior
  uv run python -m jabs_postprocess.cli.main merge-tables \
    --input-tables experiment1_grooming_bouts.csv experiment2_grooming_bouts.csv \
    --output-prefix merged_grooming

  # Auto-merge all tables in a folder, grouped by behavior  
  uv run python -m jabs_postprocess.cli.main merge-multiple-tables \
    --table-folder /path/to/experiment/tables \
    --output-prefix experiment_merged

These changes include unit tests!

$ uv run pytest tests/test_generate_behavior_tables.py
============================== test session starts ===============================
platform darwin -- Python 3.10.9, pytest-8.3.5, pluggy-1.5.0
rootdir: /Users/aberger/Projects/KumarLab/JABS-postprocess
configfile: pyproject.toml
plugins: cov-6.1.1
collected 25 items                                                               

tests/test_generate_behavior_tables.py .........................           [100%]

=============================== 25 passed in 0.53s ===============================