[hechuan9]

The IF97 boiling/dew boundary functions return records with missing fields: the Gibbs branch does not assign cv, while the region 3 Helmholtz branch does not assign cp, vt, or vp. A compiler enforcing assigned outputs rejects these calls even when a caller only needs another field.

This fills the missing properties using the existing Gibbs heat-capacity expression and the thermodynamic identities cp-cv = T*pt^2/(d^2*pd), vt = pt/(d^2*pd), and vp = -1/(d^2*pd). Previously assigned properties and the region selection are unchanged.

Adds ModelicaTest.Media.TestOnly.WaterIF97_boundaryProperties, covering both curves at 0.1, 10, 20 and 22 MPa. Heat capacities are compared to the existing Gibbs/Helmholtz boundary-property functions; volume derivatives are checked against the pressure derivatives.

Fixes #1910.

Validation on Linux at startTime=stopTime=0:

• Rumoca 590ac739: the new test fails before the change with bpro__cv is used without a value; passes after the change.
• OpenModelica 1.27.1: the new test initializes successfully and all assertions pass.
• git diff --check passes.
• No time-domain run or full library campaign was performed. Keeping this PR in draft pending CI/review.

Change size: 10 production lines and 42 test lines added in two files; no new public functions.