Improve caching metrics

[kedar389]

Tried to improve caching metrics for both backends.

• Created Dataclass that would represent Cache Stats for both memory and redis backend
• Add eviction rate, memory usage and usage saved based on the characters of prompt
• Redis received the same treatment and improved collection of these metrics in case redis instance would be used for more than TTS caching
• I Added tests but sadly CI is not configured to run them.

[kedar389]

@omChauhanDev Could you review this and we can have this discussion about this perhaps ?