refactor: move field filters (+ tests) under separate subdir (#248)

## Description
Move the field specific filters (and their tests) under separate
subdirectories.

## What problem does this change solve?
Makes it easier to see at a glance which filters only work on field or
tabular inputs.

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changes include unit tests, updates to any affected dependencies and
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Author: aaron-hopkinson

src/anemoi/transform/filters/__init__.py

@@ -10,9 +10,9 @@
 
 from typing import Any
 
-from anemoi.utils.registry import Registry
+from anemoi.transform.filters.fields import filter_registry as fields_filter_registry
 
-filter_registry = Registry(__name__)
+filter_registry = fields_filter_registry
 
 
 def create_filter(context: Any, config: Any) -> Any:
@@ -33,3 +33,6 @@ def create_filter(context: Any, config: Any) -> Any:
     filter = filter_registry.from_config(config)
     filter.context = context
     return filter
+
+
+__all__ = ["filter_registry", "create_filter"]

src/anemoi/transform/filters/fields/__init__.py

@@ -0,0 +1,13 @@
+# (C) Copyright 2026- Anemoi contributors.
+#
+# This software is licensed under the terms of the Apache Licence Version 2.0
+# which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# In applying this licence, ECMWF does not waive the privileges and immunities
+# granted to it by virtue of its status as an intergovernmental organisation
+# nor does it submit to any jurisdiction.
+
+
+from anemoi.utils.registry import Registry
+
+filter_registry = Registry(__name__)

…i/transform/filters/accum_to_interval.py …form/filters/fields/accum_to_interval.pysrc/anemoi/transform/filters/accum_to_interval.py renamed to src/anemoi/transform/filters/fields/accum_to_interval.py src/anemoi/transform/filters/accum_to_interval.py renamed to src/anemoi/transform/filters/fields/accum_to_interval.py

@@ -15,8 +15,8 @@
 import numpy as np
 
 from anemoi.transform.filters import filter_registry
-from anemoi.transform.filters.matching import MatchingFieldsFilter
-from anemoi.transform.filters.matching import matching
+from anemoi.transform.filters.fields.matching import MatchingFieldsFilter
+from anemoi.transform.filters.fields.matching import matching
 
 
 @filter_registry.register("cos_sin_from_rad")

…c/anemoi/transform/filters/apply_mask.py …i/transform/filters/fields/apply_mask.pysrc/anemoi/transform/filters/apply_mask.py renamed to src/anemoi/transform/filters/fields/apply_mask.py src/anemoi/transform/filters/apply_mask.py renamed to src/anemoi/transform/filters/fields/apply_mask.py

@@ -15,8 +15,8 @@
 import numpy as np
 
 from anemoi.transform.filters import filter_registry
-from anemoi.transform.filters.matching import MatchingFieldsFilter
-from anemoi.transform.filters.matching import matching
+from anemoi.transform.filters.fields.matching import MatchingFieldsFilter
+from anemoi.transform.filters.fields.matching import matching
 
 
 @filter_registry.register("cos_sin_mean_wave_direction")