Add 55 unit tests covering feature gaps; document micromamba dev environment

New test file (tests/test_coverage_gaps.py) covers previously untested
features: ELU/SELU/LeakyReLU activations, JSON export validation,
innovation tracker pickle support, IZ neuron overflow handling,
parallel evaluator seeded reproducibility, spawn count adjustment,
config parameter error paths, and gene equality by innovation number.

Updated CLAUDE.md to document the neat-python micromamba environment
which includes CuPy for GPU tests. This resolves the apparent 0%
GPU coverage which was caused by running tests with system Python.

Overall coverage: 90% → 97% (with micromamba env).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: CodeReclaimers

CLAUDE.md

@@ -6,18 +6,33 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 NEAT-Python is a pure-Python implementation of NEAT (NeuroEvolution of Augmenting Topologies), a method for evolving arbitrary neural networks. This project has no dependencies beyond the Python standard library and supports Python 3.8-3.14 and PyPy3.
 
+## Development Environment
+
+A micromamba environment named `neat-python` is available with all dependencies (including CuPy for GPU tests). Prefix commands with `micromamba run -n neat-python` to use it:
+
+```bash
+# Run commands in the neat-python environment
+micromamba run -n neat-python pytest tests/ -v
+micromamba run -n neat-python python examples/xor/evolve-minimal.py
+```
+
 ## Key Development Commands
 
+All commands below assume the `neat-python` micromamba environment. Prefix with `micromamba run -n neat-python` when running from outside the environment.
+
 ### Testing
 ```bash
 # Run all tests with coverage
-pytest tests/ --cov=neat --cov-report=term --cov-report=xml -v
+micromamba run -n neat-python pytest tests/ --cov=neat --cov-report=term --cov-report=xml -v
 
 # Run a single test file
-pytest tests/test_genome.py -v
+micromamba run -n neat-python pytest tests/test_genome.py -v
 
 # Run a specific test
-pytest tests/test_genome.py::TestGenome::test_mutate_add_node -v
+micromamba run -n neat-python pytest tests/test_genome.py::TestGenome::test_mutate_add_node -v
+
+# Run GPU tests (requires CuPy + NVIDIA GPU, both available in the micromamba env)
+micromamba run -n neat-python pytest tests/test_gpu.py -v
 ```
 
 ### Installation