test(hydraulics): add pFUnit test suite for FatesBstressMod

[johnpaulalex]

Description of changes

This PR adds a comprehensive pFUnit test suite (test_FatesBstress.pf) for FatesBstressMod, covering salinity transpiration stress calculations (btran_sal_stress_fates). It also updates CMake configuration to support out-of-tree isolated git worktree builds and resolves module dependencies (EDBtranMod.F90).

The test suite includes 6 targeted pFUnit test cases:

• Exact analytical assertion of transpiration wetness factor ($rresis$) under default salinity conditions.
• Upper bound cap limit verification ($rresis \le 1.0$) under zero/negative salinity edge cases.
• Transpiration stress decay verification under high salinity ($S = 0.5$ ppt).
• Sub-freezing soil layer exclusion verification ($T < T_{frz}$, ensuring frozen layers contribute 0 to stress).
• Multi-patch linked list traversal verification ($p_1 \to p_2$).
• Multi-PFT loop verification ($numpft = 2$).

Specific notes

Contributors other than yourself, if any:

• @johnpaulalex

Linked issues addressed, if any:

• None

Description of generative AI usage:

• Google Antigravity was used to write the code and tests, followed by human-guided verification.

Answer Changes & Scientific Impact

• Bit-for-Bit (B4B) with baseline master
• Roundoff-level differences only
• Expected Answer Changes (ECA)

User Interface & Namelist Changes

• Namelist / Defaults modified? No
• XML / Build script changes? Yes (CMake worktree build path updates)

Testing planned or performed, if any:

• Executed pFUnit regression tests (run_unit_tests.py -t fates_bstress)

CTSM / CESM baseline hash-tag: N/A
PR branch hash-tag: 245c55d

Requirements before merge:

• The code in this PR branch builds with no errors.
• The code in this PR branch runs with no errors.
• In-code documentation and Fortran docstrings updated.
• This PR either (a) does not create a need to update documentation or (b) includes required documentation updates. Which?: (a) Bug fix / unit test addition; no documentation updates required.