Sync tree-building with problem specifications

[BNAndras]

Update the tree-building exercise's test suite, if necessary, to include new or updated canonical test cases from the problem-specifications repository.

Use the canonical data as the source of truth, and compare it directly with our test suite rather than assuming .meta/tests.toml is an accurate representation.

Existing track-specific tests may remain if they provide useful additional coverage and, more importantly, do not conflict with canonical behavior. We want to follow the canonical data whenever it is reasonable for this track.

A canonical case with a reimplements field replaces the case identified by that field. Include only the replacement case, not the case it replaces.

Some tests may not be suitable for this track and should be intentionally omitted. Record intentional omissions under the corresponding test entry in .meta/tests.toml using:

include = false
comment = "<brief explanation of why the test is omitted>"

Some updates may require changes to .meta/Example.vb. Ensure the example solution passes the complete test suite by running:

./bin/test.ps1 tree-building

If this exercise has no canonical data upstream, discuss the appropriate next steps in this issue before making changes.

References

• Existing test suite for tree-building
• Canonical data for tree-building
• Building practice exercises
• Syncing exercise data with problem specifications