Fix CTM offset bug in multispeaker datasimulator 
# What does this PR do ?

This PR fixes inaccurate CTM time stamps from multispeaker data simulator.

**Collection**: [Note which collection this PR will affect]
ASR

# Changelog 

The function `create_new_ctm_entry`'s argument `start` should be float
Original:
start=int(start / self._params.data_simulator.sr)
Fixed:
start=float(start / self._params.data_simulator.sr)

# Usage

```python

  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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- [x] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [x] Did you write any new necessary tests?
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**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation

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## Who can review?

ASR and speaker task related contributors

# Additional Information
N.A.
