Add integration tests and update pytest markers

- Introduced a new test file `test_network_correction.py` containing comprehensive unit tests for the `NetworkIDWCorrector` and `NetworkOICorrector` classes.
- Implemented various test cases covering single and multiple observations, handling of NaN values, and validation of correction behavior.
- Added integration tests that utilize real data files to ensure the correctness of the correction algorithms in practical scenarios.
- Updated `pyproject.toml` to include a new pytest marker for integration tests.

Author: dwr-psandhu

.github/network-ec-correction.md

@@ -0,0 +1,25 @@
+# Network-Aware EC Correction — pydsm Core Algorithm
+
+See full design document in the `dsm2ui` repository:
+
+`dsm2ui/.github/network-ec-correction.md`
+
+## Summary
+
+This package provides the core algorithm:
+
+- `pydsm/analysis/network_correction.py`
+  - `NetworkCorrector` (ABC)
+  - `NetworkIDWCorrector` — directed graph, IDW weights
+  - `NetworkOICorrector` — undirected graph, OI with exponential/channel-direction kernel
+  - `exponential_kernel()`, `channel_direction_kernel()` — kernel factories
+  - `extract_channel_end_values()` — QualH5 → channel-end DataFrame
+  - `snap_stations_to_channel_ends()` — project x/y stations onto network
+
+The animation integration (`CorrectedQualH5ConcentrationReader`, CLI options,
+UI correction card) lives in `dsm2ui/animate.py` and `dsm2ui/animate_cli.py`.
+
+## Test location
+
+`pydsm/tests/test_network_correction.py` — 47 tests covering IDW, OI, both
+kernels, SPD guarantee, missing-observation handling, and real H5 integration.