fix(wcf): remove PUE double-counting; feat: error handling, config loaders, output options

[vinisha231]

Summary

This PR addresses four tracked issues with real fixes and full test coverage.

🐛 fix: remove PUE double-counting in request_usage_wcf (#230)

request_energy already embeds datacenter_pue. The previous formula multiplied by datacenter_pue a second time for the electricity-mix WUE term, inflating water impact by PUE² on that component. WUE is also defined relative to IT energy (pre-PUE), so the datacenter cooling term now divides out PUE before applying datacenter_wue.

Before: request_energy * (datacenter_wue + datacenter_pue * if_electricity_mix_wue)
After: (request_energy / datacenter_pue) * datacenter_wue + request_energy * if_electricity_mix_wue

🚨 feat: actionable error messages for new users (#100)

• ProviderNotInstalledError — includes pip install ecologits[provider] hint
• InvalidProviderError — lists all valid providers in the message
• ConfigurationError — for bad config/init state
• OpenTelemetryNotInstalledError — replaces silent logger + bare EcoLogitsError

📁 feat: load configuration from file or environment (#98)

• load_config_from_json(path) / EcoLogits.init_from_config(path)
• load_config_from_yaml(path) / EcoLogits.init_from_yaml(path) (pyyaml optional)
• load_config_from_env() / EcoLogits.init_from_env() — reads ECOLOGITS_PROVIDERS, ECOLOGITS_ELECTRICITY_MIX_ZONE, ECOLOGITS_OPENTELEMETRY_ENDPOINT

📊 feat: richer output options for impact results (#118)

• Impacts.to_dict(), Impacts.to_json(), Impacts.summary(), Impacts.__repr__
• BaseImpact.to_dict(), BaseImpact.__repr__
• RangeValue.to_dict(), __repr__, __sub__, __rsub__, __neg__, __abs__
• impacts_to_csv(impacts) — CSV export with phase/metric/value/unit columns

Other improvements

• EcoLogits.reset() classmethod for test isolation
• 4 new warning codes: electricity-mix-not-available, model-arch-deprecated, provider-data-unavailable, impact-estimate-uncertain
• All impact model classes exported from ecologits.impacts
• Fixed docstring: gpu_energy gamma coefficient was mislabelled "Beta"

Test plan

• tests/test_wcf_pue.py — WCF PUE regression tests
• tests/test_exceptions.py — exception hierarchy and message content
• tests/test_config.py — JSON, YAML, env config loaders
• tests/test_ecologits_init.py — init_from_config, init_from_env integration
• tests/test_output_options.py — to_dict, to_json, summary, __repr__
• tests/test_export.py — impacts_to_csv
• tests/test_impacts_modeling.py — BaseImpact and Impacts model methods
• Updated tests/test_range_value.py and tests/test_status_messages.py

🤖 Generated with Claude Code