Cdap integration for issue #30572

[aydinka]

Reason

Enable CDAP capabilities in the subchannel solver for SFR analyses—i.e., model breach/plume behavior and gas-blanketing effects so heat/mass transfer and cross-flow are represented more realistically during off-normal conditions.

Design

• Add LiquidMetalCDAP problem class (modules/subchannel) derived from SubChannel1PhaseProblem.
• Wire CDAP terms into axial convection/cross-flow assembly; provide inlet handling consistent with channel areas.
• Mark computeMdot(int) virtual in the base and override in CDAP to customize inlet boundary treatment without touching other problems.
• Keep defaults backward-compatible; CDAP logic is only active when problem = LiquidMetalCDAP (or equivalent app param).

Impact

• API: Backward-compatible; new class added, no removals. One base method marked virtual.
• Inputs: No changes for existing cases. New capability is opt-in via selecting the CDAP problem type.
• Behavior: Existing problems are unaffected; CDAP cases get improved inlet mass-flow distribution and plume/cross-flow coupling.
• Build/Docs/Tests: Adds new sources/headers and documentation stubs for CDAP. Unit/regression tests to follow with TPinSolver work.

Refs #30572. Depends on TPinSolver integration (tracked separately).

If this PR implements a bug fix, please create an issue for the bug and reference the issue.
-->