Align package name with directory structure for serialization package

[Copilot]

The package was declared as foundation despite residing in pkg/forging/foundation/serialization/, causing import confusion where consumers import from a .../serialization path but reference foundation.* identifiers.

Changes

• Renamed package declaration from foundation to serialization in:
  • json_serializable.go
  • json_serializable_test.go
  • serializable.go

Imports now align with package references:

import "github.com/forging-blocks-org/forging/pkg/forging/foundation/serialization"

// Now use serialization.JSONSerializable instead of foundation.JSONSerializable
obj := &serialization.JSONSerializable{Value: data}

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