fix: narrow Wall velocity validation errors

[benflexcompute]

Summary

• fix WallRotation.angular_velocity so its field metadata is treated as a description instead of a default value
• route Wall.velocity dict inputs through the tagged wall-velocity models before the tuple branch is attempted
• add a regression test for missing WallRotation.angular_velocity

Why

Missing WallRotation.angular_velocity currently produces noisy validation output:

• the field description string is parsed as a unit expression because it was accidentally used as the default value
• Wall.velocity is a union with VelocityVectorType, so dict inputs also leak tuple/validator branch errors that are irrelevant once type_name already points to WallRotation

Validation

• python -m py_compile flow360/component/simulation/models/surface_models.py tests/simulation/params/test_rotation.py
• HOME=/tmp MPLCONFIGDIR=/tmp/matplotlib /disk2/ben/SchemaMigration/Flow360/.venv/bin/python3 -m pytest -c tests/pytest.ini -rA tests/simulation/params/test_rotation.py -k 'wall_angular_velocity or missing_angular_velocity'

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Note

Low Risk
Low risk: changes only Pydantic field metadata and pre-validation for Wall.velocity, primarily affecting error reporting and dict parsing rather than solver translation logic.

Overview
Fixes WallRotation.angular_velocity so its Field string is treated as a description (not a default), restoring correct “Field required” behavior when missing.

Adds a velocity pre-validator on Wall that routes dict inputs with type_name through a TypeAdapter for tagged wall-velocity models, preventing noisy union/tuple-branch validation errors. Includes a regression test asserting the narrowed validation output for missing angular_velocity.

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