Add Buffered RNNT with LCS Merge algorithm
Signed-off-by: smajumdar <titu1994@gmail.com>

Adds an optional research notebook discussing the Longest Common Subsequence merge algorithm as used for Streaming/Buffered transducer inference.

**Collection**: [ASR]

# Changelog 
- Add optional research notebook

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