[infra] Stabilize libpng dependency download

[vikuznetsov-nvidia]

Fetch the unchanged libpng 1.6.55 tag from GitHub to avoid unreliable SourceForge mirror redirects.

Summary by CodeRabbit

• Chores
  • Updated the libpng download source to use the official GitHub release archive.
  • Updated the archive verification checksum to match the new source.

[coderabbitai]

📝 Walkthrough

Walkthrough

The libpng CMake fetch configuration now downloads the versioned release tarball from GitHub instead of SourceForge and verifies it with an updated SHA256 hash.

Changes

libpng Fetch Configuration

Layer / File(s)	Summary
Update libpng archive source cmake/ext/libpng.cmake	FetchContent_Declare(libpng) uses the GitHub v${LIBPNG_VERSION}.tar.gz archive and its corresponding SHA256 checksum.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Suggested reviewers: hrabeti-nvidia, slepichev

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: making the libpng dependency download more reliable.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch vikuznetsov/stabilize-libpng-download

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@cmake/ext/libpng.cmake`:
- Around line 37-38: Update the LIBPNG_VERSION value to a release newer than
1.6.55, specifically at least 1.6.56, and replace the URL_HASH SHA256 with the
checksum for the selected release. Keep the archive URL interpolation unchanged
so the version and checksum remain synchronized.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Enterprise

Run ID: 218f015e-27bd-4a9b-a36c-d560615cb8c4

📥 Commits

Reviewing files that changed from the base of the PR and between b8c4992 and f82cd67.

📒 Files selected for processing (1)

• cmake/ext/libpng.cmake

[github-actions]

Test Results

Status	Platform	Language	Total	Passed	Failed	Errors	Skipped
✅	Orin	C++	16	16	0	0	0
✅	Orin	Python	68	67	0	0	1
✅	Thor	C++	16	16	0	0	0
✅	Thor	Python	68	67	0	0	1
✅	x86_64	C++	16	16	0	0	0
✅	x86_64	Python	68	67	0	0	1

cuVSLAM Evaluation KPIs

Config	Dataset	ATE,%	ARE,º/m	Kabsch,	Losts,	diff ATE,%	diff ARE,º/m	diff Kabsch,	diff Losts,	FPS,Hz
x86_64-cuda12.6.3-ubuntu24.04	KITTI-STEREO_ODOM	0.8445	0.0023	2.824	0	NA	NA	NA	NA	305.8
x86_64-cuda12.6.3-ubuntu24.04	KITTI-STEREO_SLAM	0.7609	0.002	1.9764	0	NA	NA	NA	NA	178.2

Artifacts

• eval-html-report
• eval-kpis-pr
• test-results-x86_64
• docs-html
• test-results-orin
• test-results-thor