[feat]: Rename `<pf-timestamp>` to `<pf-v5-timestamp>`

[bennypowers]

Summary

Rename <pf-timestamp> to <pf-v5-timestamp> and update associated CSS custom properties to use the pf-v5 prefix.

Scope

• Rename element tag from pf-timestamp to pf-v5-timestamp
• Rename all CSS custom properties (e.g. --pf-timestamp--* to --pf-v5-timestamp--*)
• Update internal class names, imports, and type declarations

Requirements

• MUST maintain feature parity with the current <pf-timestamp> implementation
• MUST rename all public CSS custom properties
• MUST update HTMLElementTagNameMap declarations
• SHOULD provide a codemod or migration guide for downstream consumers