[BUG] Fix typo in test_topography_II and update Spremberg file paths

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Description

This PR fixes a typo in the test function name test_topography_II (previously misspelled as test_topogrphy_II) and adds model serialization verification to this test. It also updates the environment variable paths in the TestStratigraphicPile class to use a base path with PATH_TO_SPREMBERG instead of separate environment variables for each file.

Checklist

• My code uses type hinting for function and method arguments and return values.
• I have created tests which cover my code.
• The test code either 1. demonstrates at least one valuable use case (e.g. integration tests)
  or 2. verifies that outputs are as expected for given inputs (e.g. unit tests).
• New tests pass locally with my changes.

[Leguark]

• [ENH] Implement ZIP-based model serialization format #1035
• [ENH] Add grid serialization and improve binary data handling #1034
• [BUG] Fix typo in test_topography_II and update Spremberg file paths #1033 👈 (View in Graphite)
• [ENH] Add model serialization validation and refactor grid modules #1032
• [ENH] Implement binary model serialization with compression #1031
• main

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Graphite Automations

"Add gempy label" took an action on this PR • (05/22/25)

1 label was added to this PR based on Miguel de la Varga's automation.

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Merge activity

• May 25, 7:09 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• May 25, 7:13 AM UTC: Graphite couldn't merge this pull request because a downstack PR [ENH] Implement binary model serialization with compression #1031 failed to merge.
• May 25, 7:18 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• May 25, 7:22 AM UTC: Graphite couldn't merge this pull request because a downstack PR [ENH] Implement binary model serialization with compression #1031 failed to merge.
• May 25, 7:26 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• May 25, 7:28 AM UTC: The Graphite merge of this pull request was cancelled.
• May 25, 7:37 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• May 25, 7:40 AM UTC: Graphite couldn't merge this pull request because a downstack PR [ENH] Add model serialization validation and refactor grid modules #1032 failed to merge.
• May 25, 7:56 AM UTC: Graphite couldn't merge this PR because it failed for an unknown reason.