feat(nws, normalizers): add NWS hourly forecast normalization and enforce canonical float rounding

- Implement full NWS hourly forecast normalizer (raw.nws.hourly.forecast.v1 → weather.forecast.v1)
- Add GeoJSON forecast types and helpers for NWS gridpoint hourly payloads
- Normalize temperatures, winds, humidity, PoP, and infer WMO condition codes from forecast text/icons
- Treat forecast IssuedAt as EffectiveAt for stable, dedupe-friendly event IDs

- Introduce project-wide float rounding at normalization finalization
  - Round all float values in canonical payloads to 2 decimal places
  - Apply consistently across pointers, slices, maps, and nested structs
  - Preserve opaque structs (e.g., time.Time) unchanged

- Add SchemaRawNWSHourlyForecastV1 and align schema matching/comments
- Clean up NWS helper organization and comments
- Update documentation to reflect numeric wire-format and normalization policies

This establishes a complete, deterministic hourly forecast pipeline for NWS
and improves JSON output stability across all canonical weather schemas.

internal/normalizers/common/doc.go

@@ -11,39 +11,9 @@
 //   - minimal abstractions (prefer straightforward functions)
 //   - easy to unit test
 //
-// What belongs here
-// -----------------
-// Put code in internal/normalizers/common when it is:
-//
-//   - potentially reusable by more than one provider
-//   - provider-agnostic (no NWS/OpenWeather/Open-Meteo specific assumptions)
-//   - stable, small, and readable
-//
-// Typical examples:
-//   - unit conversion helpers (°F <-> °C, m/s <-> km/h, hPa <-> Pa, etc.)
-//   - json.RawMessage payload extraction helpers (with good error messages)
-//   - shared parsing helpers (timestamps, simple numeric coercions)
-//   - generic fallbacks (e.g., mapping a human text description into a coarse canonical code),
-//     so long as the logic truly applies across providers
-//
-// What does NOT belong here
-// -------------------------
-// Do NOT put the following in this package:
-//
-//   - Normalizer implementations (types that satisfy feedkit/normalize.Normalizer)
-//   - provider-specific JSON structs or mapping logic (put those under
-//     internal/normalizers/<provider>/)
-//   - network or filesystem I/O (sources fetch; normalizers transform)
-//   - code that depends on event.Source naming, config fields, or driver-specific params
-//
-// Style and API guidelines
-// ------------------------
-//   - Prefer small, single-purpose functions.
-//   - Keep function names explicit (avoid clever generic “DoThing” helpers).
-//   - Return typed errors with context (include schema/field names where helpful).
-//   - Keep dependencies minimal: standard library + weatherfeeder packages only.
-//   - Add unit tests for any non-trivial logic (especially parsing and fallbacks).
-//
-// Keeping this clean matters: common is shared by all providers, so complexity here
-// multiplies across the project.
+// Numeric wire policy
+// -------------------
+// Canonical payloads are intended for sinks/serialization. To keep output stable and readable,
+// weatherfeeder rounds floating-point values in canonical payloads to a small, fixed precision
+// at finalization time (see round.go).
 package common