Hybrid RNNT-CTC Prompted Parakeet Model support

[nithinraok]

PR: #14561

PIC: @ealbasiri

Adds support for Hybrid RNNT-CTC BPE Model with Prompt Feature (EncDecHybridRNNTCTCBPEModelWithPrompt), enabling flexible ASR and AST tasks through prompt-based conditioning.

Key Features

• Architecture: Hybrid RNNT-CTC model with prompt vector conditioning
  • Prompt vector (one-hot encoded) is concatenated to ASR embeddings from FastConformer
  • Concatenated vector is fed into decoder for prompt-aware processing
• Tasks: model supports both ASR and AST
• Inference Modes: Supports both buffered streaming and offline inference
• Scalable Design: Can support multilingual ASR and AST tasks

Prompt-Based Conditioning

• Target language prompt: Required input that conditions the model behavior
• Source language detection: Not required - model automatically handles source language
• Task determination:
  • Same source/target → ASR (transcription)
  • Different source/target → AST (translation)
• Supported languages: multilingual ASR/AST