Use full URL when redirecting to snapshots, for consistency with primary redirects

[eddyashton]

First change to solidify snapshot fetching, hoping to be iteratively backportable:

Change the redirect response header from Location: /node/snapshot/XXX to Location: https://1.2.3.4/node/snapshot/XXX. This prevents the client returning to the load balancer and being silently redirected to a different node, and is consistent with other nodefrontend-specific redirects.

Requires a frustratingly large diff, I'll justify/explain that inline.

[Copilot]

Pull Request Overview

This PR changes snapshot redirect responses to use full URLs instead of relative paths, ensuring clients connect directly to the correct node rather than potentially being redirected through a load balancer. The change updates both the redirect generation logic and the client-side handling to use full URLs.

• Modifies the node frontend to generate full HTTPS URLs in redirect responses for snapshot endpoints
• Updates the snapshot fetching client code to properly handle redirect URLs using CURL's built-in redirect following
• Updates tests to validate the new full URL redirect behavior

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/node/rpc/node_frontend.h	Generates full HTTPS URLs for snapshot redirects using node's published address
src/snapshots/fetch.h	Refactors redirect handling to use CURL's CURLINFO_REDIRECT_URL and follows redirects iteratively
src/http/curl.h	Changes URL parameter from rvalue reference to const reference for reusability
tests/e2e_operations.py	Updates tests to expect full URLs in redirect responses and uses path for subsequent requests

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[achamayou]

This definitely goes in the right direction, but I think we want a clear error when we have an interface mismatch. Also I wonder if we can do something more efficient (see comment above).

[achamayou]

Poked the auto-merge in the hope of unsticking the CLA, but to no avail. A changelog entry would be helpful.