Fix PNTS section bounds validation

[atirna]

Description

Reject PNTS tiles when the declared feature and batch table sections extend past the tile's byteLength. The check uses a 64-bit aggregate before any section spans are created, covering both vulnerable paths.

Issue number or link

Fixes #1425

Author checklist

• I have submitted a Contributor License Agreement (only needed once).
• I have done a full self-review of my code.
• I have updated CHANGES.md with a short summary of my change (for user-facing changes).
• I have added or updated unit tests to ensure consistent code coverage as necessary.
• I have updated the documentation as necessary.

Testing plan

• cmake --build build --target cesium-native-tests --parallel 4
• build/CesiumNativeTests/cesium-native-tests --test-case='Rejects PNTS sections that extend past the declared byte length' (1 test case, 8 assertions)
• clang-format --dry-run --Werror on the changed C++ source and test

[j9liu]

Thanks @atirna for the PR! We still need a signed Contributor License Agreement from you in order to review your code. Once that is signed, we can put this on our review queue and take a look!

[atirna]

have submitted the CLA form