refactor: refactor cache system to support generics and arbitrary value types

[appleboy]

• Refactor the cache system to use generics, enabling support for any value type instead of just int64
• Replace all cache interfaces and implementations with generic versions, updating construction and method signatures accordingly
• Change Redis cache serialization from string conversion to JSON encoding/decoding for compatibility with arbitrary types
• Update cache-aside logic to use type assertion for optimized stampede protection when available, with generic fallback
• Revise all related tests and helper functions to utilize the generic cache pattern

[Copilot]

Pull request overview

This pull request refactors the cache system to support generics, enabling storage of arbitrary value types instead of being limited to int64. The refactor replaces string-based serialization with JSON encoding for Redis implementations and separates the cache-aside pattern into an optional interface with a generic fallback helper.

Changes:

• Introduced generic type parameter T to all cache interfaces and implementations (Cache[T any], MemoryCache[T any], RueidisCache[T any], RueidisAsideCache[T any])
• Replaced string conversion (strconv) with JSON marshaling for Redis cache serialization/deserialization
• Split GetWithFetch into an optional CacheWithFetch[T] interface for optimized implementations and a standalone generic helper function for basic cache-aside support

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/cache/interface.go	Converted Cache interface to generic Cache[T any], added CacheWithFetch[T any] interface for optimized cache-aside, and introduced GetWithFetch helper function
internal/cache/memory.go	Updated MemoryCache to generic MemoryCache[T any], removed GetWithFetch method (now uses generic helper)
internal/cache/rueidis.go	Converted RueidisCache to generic type, replaced strconv with json.Marshal/Unmarshal, removed GetWithFetch method
internal/cache/rueidis_aside.go	Converted RueidisAsideCache to generic type, updated GetWithFetch to implement CacheWithFetch interface, replaced strconv with json encoding
internal/cache/cache_test.go	Updated all test constructors to use type parameters (e.g., NewMemoryCacheint64), renamed GetWithFetch tests to reflect standalone function
internal/metrics/cache.go	Updated CacheWrapper to use Cache[int64], added type assertion logic to prefer CacheWithFetch when available
internal/metrics/cache_test.go	Updated all test cache constructors to use type parameter [int64]
internal/bootstrap/cache.go	Updated cache initialization to specify type parameter [int64] for all cache constructors
internal/bootstrap/bootstrap.go	Updated MetricsCache field type to Cache[int64]
internal/bootstrap/server.go	Updated function signatures to accept Cache[int64] type

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