odb: implement wire bbox test in test_block (Python + TCL)

[rohithsiddi]

Summary

Fill in the # TODO ADD WIRE stub that has been present in block_placement
step 5 of both test_block.py and test_block.tcl. Add the corresponding
test_bbox5 test in both files to verify that a dbWire correctly expands
the block bounding box.

• Creates a net and encodes a horizontal wire from (0, 4500) to (3000, 4500)
  on layer L1 (width 200) using dbWireEncoder
• xMax in test_bbox5 is 3100, not 3000: each wire endpoint is extended by
  half the wire width (100) in the direction of travel

Test plan

• ctest -R "odb\.test_block" -V — 7 Python tests pass, TCL test passes
• ctest -R "odb\.test_destroy" -V — existing tests unaffected

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[gemini-code-assist]

Code Review

This pull request adds a test case for wire bounding boxes in Python and TCL. My review focuses on improving code maintainability by replacing magic numbers with named constants, in line with the repository's general rules.