TST: cover geospatial extent conversions

[ting-hong-shieh]

Summary

This adds unit coverage for the three geospatial extent helpers in rocketpy.tools:

• known spherical Mercator coordinates for mercator_to_wgs84;
• a local → WGS84 → Mercator → local round trip; and
• southwest and northeast extents that verify coordinate ordering and offset signs.

The change is test-only and follows the small, deterministic coverage slices discussed in #709.

Coverage

The base and head measurements used the same command and inputs.

rocketpy/tools.py	Base	Head
Statements	313	313
Covered	121	149
Missed	192	164
Coverage	39%	48%
tests/unit/test_tools.py results	23 passed	28 passed

Merge base: 2f9a44b92e5288145ba0c1e93f88aef57590437c
Head: 58f9981f314f74e207a1523f652e57d70b778cc3

Validation

.venv/bin/python -m coverage run --source=rocketpy -m pytest tests/unit/test_tools.py -q
.venv/bin/python -m coverage report -m rocketpy/tools.py
.venv/bin/ruff check tests/unit/test_tools.py
.venv/bin/ruff format --check tests/unit/test_tools.py

Head results: 28 passed with five pre-existing warnings; Ruff passed and the file was already formatted.

The round-trip assertion allows an absolute error of 0.2 m. The fixtures exercise the spherical Mercator equations with an explicit radius of 6,378,137 m; they do not add ellipsoidal-Earth or projection-domain behavior.

Environment

Component	Version
Python	3.12.6
RocketPy	1.13.0 (develop checkout)
NumPy	2.5.2
SciPy	1.18.0
pytest	9.1.1
OS	macOS 26.5.2
Architecture	arm64

Closes no issue; contributes to #709.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.51%. Comparing base (e0ff281) to head (58f9981).
⚠️ Report is 60 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1158      +/-   ##
===========================================
+ Coverage    82.18%   83.51%   +1.33%     
===========================================
  Files          122      130       +8     
  Lines        16355    17082     +727     
===========================================
+ Hits         13441    14266     +825     
+ Misses        2914     2816      -98     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.