refactor: Standardize meshdata attribute names

[anas-ibrahem]

Summary

This PR standardizes mesh attribute names across the codebase.
coords, tria, quad, values are now the canonical API on all mesh classes, which fixes AttributeError issues when passing EuclideanMesh2D objects to utility functions.

Resolves #226

Changes

• base.py — coords is now the main property; coord is kept as a deprecated alias.
• mesh.py — tria, quad, and values replace triangles, quads, and value. Old names remain as deprecated aliases. Helpers updated.
• collector.py — Switched to tria, coords, values.
• combine_geom.py — Switched to coords in CRS reprojection.
• test_mesh.py — Updated .value to .values.

Testing & Results

python -m pytest tests/ -v
# result: 175 passed, 8 skipped

#verify deprecated names warn and new names are silent with simple assertions
python -c "
import warnings, numpy as np
from ocsmesh.internal import MeshData
from ocsmesh.mesh.mesh import EuclideanMesh2D

md = MeshData(coords=np.array([[0,0],[1,0],[0.5,1.0]]), tria=np.array([[0,1,2]]))
m = EuclideanMesh2D(md)

with warnings.catch_warnings(record=True) as w:
    warnings.simplefilter('always')
    _ = m.coord; _ = m.triangles; _ = m.quads; _ = m.value
    assert len(w) == 4 and all(issubclass(x.category, DeprecationWarning) for x in w)
    print('PASS: all 4 old names warn correctly')

with warnings.catch_warnings(record=True) as w:
    warnings.simplefilter('always')
    _ = m.coords; _ = m.tria; _ = m.quad; _ = m.values
    assert len(w) == 0
    print('PASS: new canonical names produce no warnings')
"

Note*
I investigated the 8 skipped tests. They are pre-existing, intentional skips unrelated to our changes ,all 8 are conditionally skipped because I am running the test suite on Windows.

• test_avg_filter_nomask
• test_avg_filter_masked_nanfill
• test_avg_filter_masked_nonnanfill
• test_add_patch
• test_hfunraster_initial_value_logic
• test_execution_mode_property
• test_work_dir_cleanup
• test_serial_vs_parallel_equivalence