[Flight] Forward the current environment when forwarding I/O entries

[sebmarkbage]

If we're forwarding I/O entries from one environment to another and we hit entries with null environment that suggests it's client entries. Like scripts or RSC stream entries loaded into the current server environment. From the perspective of the consuming client, those are not "client" entries but rather I/O that happened on the server.

[react-sizebot]

Comparing: 83ea655...9c433e5

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.js	=	6.68 kB	6.68 kB	=	1.83 kB	1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	605.41 kB	605.41 kB	=	107.21 kB	107.21 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.69 kB	6.69 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	664.38 kB	664.38 kB	=	117.09 kB	117.09 kB
facebook-www/ReactDOM-prod.classic.js	=	688.25 kB	688.25 kB	=	121.13 kB	121.13 kB
facebook-www/ReactDOM-prod.modern.js	=	678.67 kB	678.67 kB	=	119.48 kB	119.49 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against 9c433e5