fix(files): bound SeekableHttpStream reads by Content-Range

[joshtrichards]

• Resolves: [Bug]: SeekableHttpStream Relies on Connection Close Instead of Content-Length, Causing 60s Timeout #58276

Summary

Harden SeekableHttpStream range handling by making the resource size declared in Content-Range authoritative.

The key read-boundary change is:

$remaining = $this->totalSize - $this->offset;
$ret = fread($stream, min($count, $remaining));

Reads are now limited to the remaining bytes in the remote resource, so the wrapper no longer requests data beyond the logical end simply because an HTTP connection remains open.

The second commit hardens Content-Range validation through a dedicated helper and makes stream lifecycle and reconnect failure handling more explicit. It also ensures that the total resource size remains consistent across range requests.

Logical EOF is determined from the declared resource size rather than transport connection closure. No additional feof() check is introduced, since probing a socket for transport-level EOF could add blocking behavior. A response shorter than its declared Content-Range remains governed by the existing PHP stream semantics.

This addresses the timeout reported in #58276 while also improving general range-stream correctness and adding focused explicit test coverage.

TODO

• Backport?

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI