Renaming to isPrividium

[tomimor]

🌟 Feature Request

📝 Description

Rename the computed property 'prividium' to 'isPrividium' in the Prividium Block Explorer component. This change affects the boolean computed property that determines the Prividium state and should be aligned between backend and frontend Prividium implementations.

🤔 Rationale

This renaming follows better naming conventions for boolean properties by using the 'is' prefix. This makes the code more readable and self-documenting, as it clearly indicates that the property returns a boolean value.

📋 Additional Context

Originally posted by @JackHamer09 in https://github.com/matter-labs/block-explorer/pull/430#discussion_r2098646458