Add DiFluid Microbalance BLE scale support

[FabianSperrle]

Add DiFluid Microbalance BLE scale support

Summary

Adds a new DIFLUID scale_type so the library can read weight from a DiFluid Microbalance (and, by protocol, the Microbalance Ti). It slots into the existing per-type pattern (name match → service discovery → notify parser → tare), so downstream consumers like CleverCoffee need no changes beyond selecting the Bluetooth scale type.

Motivation

I ended up with a DiFluid Microbalance — a hand-me-down from a family member who wasn't using it — and wanted to run it as a brew scale, but the library didn't support it. Unlike the existing scales it ships a dual-channel GATT (one encrypted, one cleartext), which is why a naive connection only ever sees ciphertext — this PR documents and handles that.

How it works (protocol)

The Microbalance exposes data service 000000EE-0000-1000-8000-00805F9B34FB with two characteristics:

• FF01 — encrypted channel (emits DA DA … ciphertext; ignored)
• AA01 — cleartext channel, notify and write (used here)

Both are on by default on current firmware; no DiFluid-server/app handshake is required, so an offline ESP32 can read weight directly.

Flow once connected on AA01:

1. Write DF DF 01 00 01 01 C1 (Func 1 / Cmd 0 = Auto Send on) — the scale does not stream until asked. No periodic heartbeat is needed afterwards.
2. The scale pushes ~5 Hz sensor notifications:

DF DF 03 00 0D | W0 W1 W2 W3 | flow(2) | time(2) | timestamp(4) | unit | checksum
index:   0..4     5  6  7  8     9 10     11 12     13 14 15 16     17     18

• Weight = signed big-endian int32 at offset 5, ×0.1 g.
• Checksum = sum(all preceding bytes) & 0xFF (a byte-sum, not XOR).
• Two other frames also arrive on AA01 and are excluded by the parse guards: the Func 1 auto-send echo, and the Func 3 / Cmd 5 device-status frame (pData[3] == 0x05).

Tare maps to a single power-button click: DF DF 03 02 01 01 C5 (Func 3 / Cmd 2).

Implementation notes

• Matched by advertised-name prefix MICROBALANCE plus discovery of service 000000EE.
• Skips the Acaia IDENTIFY / NOTIFICATION_REQUEST handshake (like GENERIC) and instead sends the auto-send-enable on connect; heartbeatRequired() stays false.
• DiFluid command writes use write-with-response (the AA01 characteristic advertises Write-with-response).
• Weight uses a signed BE int32 so post-tare negatives work without a separate sign byte.
• On-scale timer is intentionally stubbed (no-op branches in startTimer/stopTimer/resetTimer) so DiFluid never receives Acaia timer bytes — the timer command bytes aren't verified yet.
• Grams only (matches the library's existing limitation).

Testing

• Protocol reverse-engineered and confirmed live with nRF Connect on a real Microbalance 299172 (full GATT capture, auto-send enable, weight + negative/post-tare frames, all checksum-validated).
• Compiles in the CleverCoffee firmware (PlatformIO, az-delivery-devkit-v4, esp32) — build green.
• Runs on hardware: connects and reports live weight via CleverCoffee.

Limitations / follow-ups

• Branch is based on tag v4.0.1; may need a rebase onto develop.
• Microbalance Ti is not physically tested. The DiFluid SDK docs suggest a shared protocol; if a Ti uses a different service UUID (the docs hint at 000000DD), discovery would need that UUID added. The MICROBALANCE name gate already covers its name.
• On-scale timer not implemented (see above).

Checklist

• New scale_type follows the existing discovery/parse/tare structure
• No changes required in consumer firmware
• Verified on real hardware
• Microbalance Ti verified (no device)
• On-scale timer commands