Add Kannada (kn-IN) G2P support for TTS

[jasro23]

• Add KannadaG2p class with hybrid dictionary + rule-based IPA conversion
• Add Kannada grapheme and IPA character sets to ipa_lexicon.py
• Add kn-IN locale support with punctuation handling
• Include lexicon with 4K Kannada words
• Add test script with assertions for validation

The G2P module handles:

• All Kannada vowels, consonants, matras (dependent vowels)
• Virama (halant), anusvara, visarga
• Anusvara place assimilation based on following consonant

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What does this PR do ?

Add Kannada (kn-IN) G2P support for TTS

Collection: [TTS]

Changelog

• Add KannadaG2p class in nemo/collections/tts/g2p/models/kn_in_ipa.py for Kannada grapheme-to-phoneme conversion
• Add Kannada grapheme and IPA character sets to ipa_lexicon.py
• Add kn-IN to supported locales with Kannada-specific punctuation
• Add pronunciation dictionary with 4264 Kannada words (kn_IN_nv260318.dict)
• Add Kannada G2P unit tests to test_tts_tokenizers.py

Usage

• You can potentially add a usage example below

# Add a code snippet demonstrating how to use this 

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Additional Information

• Related to # (issue)