FIX: Copy the owid in the FodId constructor, not just fromOwid

[oleksandrlazarenko-pi]

Follow-up to the 51Did reader (#166), addressing a review point from Eugene on the PHP port (pipeline-php-did#2) and propagating the fix for cross-port consistency (per the review guidelines).

Problem

FodId.fromOwid already copies the owid, but the public constructor new FodId(owidInstance) still aliased the caller's instance (this._owid = owidInstance). An owid instance is mutable, so new FodId(o) followed by mutating o reintroduced exactly the cached-hash vs live-payload desync that fromOwid was fixed to prevent. Java already avoids this (its constructor is private and Owid is final); Node and Python shared the gap.

Fix

Copy the owid in the constructor (re-parse from its base64), so every construction path is decoupled from the caller's instance:

this._owid = new owid(owidInstance.data);

fromOwid now simply delegates to the constructor (single copy site).

Test

Adds a constructor is decoupled from the source owid test (mirrors the existing fromOwid decouple test, but via the public constructor). Full suite: 33/33 pass.