Introduce the BatteryPool, and implement power bounds calculation for the pool (#32)

This PR introduces a high-level `BatteryPool` API and supporting
telemetry/bounds trackers to compute aggregated dispatch power bounds
for a pool of batteries (grouped by inverter↔battery topology), along
with a refactor of formula streaming APIs to use metric generics.

**Changes:**
- Add battery pool telemetry tracking (healthy/unhealthy partitioning
with latest telemetry) and bounds aggregation across inverter-battery
groups.
- Expose `Microgrid`/`BatteryPool` as public high-level APIs and add a
bounds example.

Author: shsms

RELEASE_NOTES.md

@@ -28,6 +28,14 @@
 
 - The resampler's `max_age_in_intervals` has also become configurable, through `LogicalMeterConfig`.
 
+- The `Quantity` trait now exposes numeric operations (`abs`, `floor`, `ceil`, `round`, `trunc`, `fract`, `is_nan`, `is_infinite`, `min`, `max`) as trait methods, so they can be used in generic code over any `Quantity` (including `f32` and all quantity types).
+
+- The `Quantity` trait now provides associated `MIN` and `MAX` constants.
+
+- New `BatteryPool` type (accessible via `Microgrid::battery_pool`) exposing:
+  - `power()` — a `Formula<Power>` for the pool's aggregated power.
+  - `power_bounds()` — a `broadcast::Receiver<Vec<Bounds<Power>>>` tracking the pool's power bounds.
+
 ## Bug Fixes
 
 <!-- Here goes notable bug fixes that are worth a special mention or explanation -->

examples/bounds.rs

@@ -0,0 +1,34 @@
+// License: MIT
+// Copyright © 2026 Frequenz Energy-as-a-Service GmbH
+
+use chrono::TimeDelta;
+use frequenz_microgrid::Microgrid;
+use frequenz_microgrid::{Error, LogicalMeterConfig};
+use tracing_subscriber::{
+    EnvFilter,
+    fmt::{self},
+    prelude::*,
+};
+
+#[tokio::main]
+async fn main() -> Result<(), Error> {
+    tracing_subscriber::registry()
+        .with(EnvFilter::new("info,frequenz_microgrid=warn"))
+        .with(fmt::layer().with_file(true).with_line_number(true))
+        .init();
+
+    let microgrid = Microgrid::try_new(
+        "http://[::1]:8800",
+        LogicalMeterConfig::new(TimeDelta::try_seconds(1).unwrap()),
+    )
+    .await?;
+
+    let mut battery_pool = microgrid.battery_pool(None)?;
+    let mut bounds_rx = battery_pool.power_bounds();
+
+    while let Ok(bounds) = bounds_rx.recv().await {
+        tracing::info!("Battery pool active-power bounds: {:?}", bounds);
+    }
+
+    Ok(())
+}