Add optional "Maximum zoom extents" for xyz algorithms

[nyalldawson]

Description

(builds off #67439)

Allows users to specify subextents of the tiles to have greater detail (higher zoom level), allowing for more tiles to be
generated in areas of greater interest.

AI tool usage

• AI tool(s) (Copilot, Claude, or something similar) supported my development of this PR. See our policy about AI tool use. Use of AI tools must be indicated. Failure to be honest might result in banning.

[qgis-bot]

@nyalldawson
This pull request has been tagged as requiring documentation.

A documentation ticket will be opened at https://github.com/qgis/QGIS-Documentation when this PR is merged.

Please update the description (not the comments) with helpful description and screenshot to help the work from documentors.
Also, any commit having [needs-doc] or [Needs Documentation] in will see its message pushed to the issue, so please be as verbose as you can.

Thank you!

[qgis-bot]

@nyalldawson

This pull request has been tagged for the changelog.

• The description will be harvested so please provide a "nearly-ready" text for the final changelog
• If possible, add a nice illustration of the feature. Only the first one in the description will be harvested (GIF accepted as well)
• If you can, it's better to give credits to your sponsor, see below for different formats.

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[github-actions]

🪟 x64-windows — ⚠️ vcpkg failed before producing per-port logs

vcpkg returned a non-zero exit code but no port left a parseable buildtree. This usually means a portfile-execute abort (e.g. find_library REQUIRED, vcpkg_extract_source_archive download failure), or a vcpkg-internal error such as a missing tool or registry/baseline mismatch.

Look at the artifacts and the workflow log:

📑 Download full build-logs-x64-windows artifact · 🔧 Workflow run · 📌 Commit ebf0fde

🍎 MacOS Qt6 builds

Download MacOS Qt6 builds of this PR for testing.
This app is not notarized, run sudo xattr -d com.apple.quarantine /Applications/QGIS*.app to avoid the warning
(Built from commit ebf0fde)