[Workers] RPC tracing for sessions + calls

[apeacock1991]

Add a changelog entry and describe RPC session and call spans for Workers and Durable Objects.

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.

[cloudflare-workers-and-pages]

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[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
/src/assets/images/workers/	@GregBrimble, @irvinebroque, @MattieTK, @vy-ton, @WalshyDev, @cloudflare/deploy-config, @cloudflare/workers-docs, @cloudflare/workers-runtime-1, @cloudflare/wrangler, @cloudflare/product-owners
/src/content/changelog/workers/	@GregBrimble, @irvinebroque, @korinne, @MattieTK, @mikenomitch, @vy-ton, @WalshyDev, @cloudflare/deploy-config, @cloudflare/dev-plat-leads, @cloudflare/workers-docs, @cloudflare/workers-runtime-1, @cloudflare/wrangler, @cloudflare/pm-changelogs, @cloudflare/product-owners
/src/content/docs/workers/observability/	@irvinebroque, @mikenomitch, @nevikashah, @vy-ton, @cloudflare/product-owners

[github-actions]

Preview URL: https://6ed2d12d.preview.developers.cloudflare.com
Preview Branch URL: https://apeacock-document-jsrpc-session-spans.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/changelog/post/2026-09-10-javascript-rpc-session-spans/	https://apeacock-document-jsrpc-session-spans.preview.developers.cloudflare.com/changelog/post/2026-09-10-javascript-rpc-session-spans/
https://developers.cloudflare.com/workers/observability/traces/spans-and-attributes/	https://apeacock-document-jsrpc-session-spans.preview.developers.cloudflare.com/workers/observability/traces/spans-and-attributes/

[irvinebroque]

nice!

wonder what we should add to Durable Objects docs to make clear to humans/agents that tracing even possible

same with cloudflare/skills (pointing back to docs)