Motivation

Added support for dictionary-like operations directly on ProcessingModule objects. Currently, users need to access the data_interfaces attribute to get information about the module's contents (e.g., len(module.data_interfaces)). This PR implements dictionary-like methods on ProcessingModule itself, making the API more intuitive and consistent with Python's container conventions.

This implements the feature requested in #1993 to support operations like len(processing_module) directly.

How to test the behavior?

from pynwb import NWBFile
from pynwb.base import TimeSeries
import datetime

# Create an NWB file with a processing module
nwbfile = NWBFile(
    session_description='demonstrate module dict operations',
    identifier='ABC123',
    session_start_time=datetime.datetime.now(datetime.timezone.utc)
)

behavior_module = nwbfile.create_processing_module(
    name='behavior',
    description='behavioral data'
)

# Add some time series
ts1 = TimeSeries(name='series1', data=[1, 2, 3], unit='m', rate=1.0)
ts2 = TimeSeries(name='series2', data=[4, 5, 6], unit='m', rate=1.0)

behavior_module.add(ts1)
behavior_module.add(ts2)

# Test new dictionary-like operations
print(len(behavior_module))  # 2
print(list(behavior_module.keys()))  # ['series1', 'series2']
print(list(behavior_module.values()))  # [<TimeSeries 'series1'>, <TimeSeries 'series2'>]

for name, interface in behavior_module.items():
    print(f"{name}: {len(interface.data)} samples")

Checklist
[x] Did you update CHANGELOG.md with your changes?
[x] Have you checked our Contributing document?
[x] Have you ensured the PR clearly describes the problem and the solution?
[x] Is your contribution compliant with our coding style? This can be checked running ruff check . && codespell from the source directory.
[x] Have you checked to ensure that there aren't other open Pull Requests for the same change?
[x] Have you included the relevant issue number using "Fix #1993" notation where XXX is the issue number? By including "Fix #1993" you allow GitHub to close issue #1993 when the PR is merged.
Fix #1993