[BugFix] Fix multi-processing bug in data simulator
# What does this PR do ?

Fix multi-processing bug in data simulator

**Collection**: 
ASR 

# Changelog 
- Add specific line by line info of high level changes in this PR.
- Changed silence sampling logic to follow overlap sampling logic
- Changed perturbator config structure to include `add_xxx_aug` in side `xxxxxx_augmentor`
- Some comment changes
- Fixed annotation file writing mechanism to fix multi-processing issue.
- Added more unit-tests for util functions 

# Usage

```python
This script creates a synthetic diarization session using the provided audio dataset with ctm files.
Usage:
  python <NEMO_ROOT>/tools/speech_data_simulator/multispeaker_simulator.py  \
    num_workers=10 \
    data_simulator.random_seed=42 \
    data_simulator.manifest_filepath=manifest_with_alignment_file.json \
    data_simulator.outputs.output_dir=./simulated_data \
    data_simulator.outputs.output_filename=sim_spk2_sess20 \
    data_simulator.session_config.num_sessions=1000 \
    data_simulator.session_config.num_speakers=2 \
    data_simulator.session_config.session_length=20 \
    data_simulator.background_noise.add_bg=False \
    data_simulator.background_noise.background_manifest=background_noise.json \
    data_simulator.background_noise.snr=40 \

Check out parameters in ./conf/data_simulator.yaml.
```

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**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation

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# Additional Information
* Related to # (issue)
