odb: make 3DBlox connection region check direction-aware

[osamahammad21]

Summary

• Make the 3DBlox connection region check direction-aware: the declared top region must face down and the declared bot region must face up
• Split geometric failures into specific messages: no XY overlap, no Z overlap (internal_ext), and surface gap vs connection thickness (with values)
• Swap top/bottom regions of unfolded connections when the holding chip is Z-mirrored so the unfolded model reflects world orientation
• Fix checker unit-test fixtures that declared connections backwards; add tests for the swapped-declaration and Z-mirrored assembly cases

Type of Change

• New feature

Impact

• check_3dblox now flags connections whose top/bot declaration contradicts the physical stackup; invalid-connection messages state the exact failure reason

Verification

• I have verified that the local build succeeds (./etc/Build.sh).
• I have run the relevant tests and they pass.
• My code follows the repository's formatting guidelines.
• I have included tests to prevent regressions.
• I have signed my commits (DCO).

Related Issues

Closes #10836

[gemini-code-assist]

Code Review

This pull request refactors the 3D-Blox connection validation logic by introducing a ConnectionStatus enum to provide more detailed error messages for invalid connections (such as invalid stacking direction, XY overlap, Z overlap, or thickness mismatch). It also updates dbUnfoldedBuilder to handle Z-mirroring of assemblies by swapping top and bottom regions when parent_xform.isMirrorZ() is true, and updates/adds corresponding unit tests. There are no review comments, so I have no feedback to provide.

[maliberty]

Is it ok for chips to touch with no defined region?

[osamahammad21]

This condition does not really mean that. This condition is checking if the defined connection in 3dbx has at least one null region (~)

According to the 3dblox standard, it is allowed to have the bottom region as null, but it doesn't allow the top region to be null. A connection to a null region defines the anchor point of the whole design as it is a connection to the virtual plane.

In this PR, I am not tackling the issue of allowing an empty top region, I am keeping the previous logic as is and incorporating the new violation kInvalidDirection