Feature: Add COBS-encoded float32 support

[SJ7F]

Summary

This pull request adds support for decoding float32 values encoded with COBS. Each COBS packet can contain any number of float32 values, each updating a different channel.

Motivation & Context

Allows for faster data logging.
COBS support was listed on the roadmap.

Changes

• Added dropdown in ConnectModal to select between the ascii (original mode, default) and cobs-f32 modes.
• Added COBS decoding logic

How to Test

Run the following code (requires Arduino.h) on a microcontroller (such as the esp32), and then connect to it using this serial plotter in COBS float32 mode. It should plot three sine waves.

(disclaimer: this test code was written by GPT-5)

#include <Arduino.h>

// Simple COBS encoder
size_t cobsEncode(const uint8_t *input, size_t length, uint8_t *output) {
  size_t read_index = 0, write_index = 1, code_index = 0;
  uint8_t code = 1;

  while (read_index < length) {
    if (input[read_index] == 0) {
      output[code_index] = code;
      code_index = write_index++;
      code = 1;
      read_index++;
    } else {
      output[write_index++] = input[read_index++];
      code++;
      if (code == 0xFF) {
        output[code_index] = code;
        code_index = write_index++;
        code = 1;
      }
    }
  }

  output[code_index] = code;
  return write_index;
}

void setup() {
  Serial.begin(115200);
  while (!Serial);
}

void loop() {
  static uint32_t t = 0;

  // Generate three float values varying with sine waves
  float f1 = sinf(t * 0.01f) * 1.0f;       // amplitude 1.0
  float f2 = sinf(t * 0.008f + 1.0f) * 2.0f; // amplitude 2.0, phase shifted
  float f3 = sinf(t * 0.012f + 2.0f) * 0.5f; // amplitude 0.5, phase shifted

  // Pack floats into a contiguous buffer
  uint8_t rawData[12];
  memcpy(rawData, &f1, 4);
  memcpy(rawData + 4, &f2, 4);
  memcpy(rawData + 8, &f3, 4);

  // Encode with COBS
  uint8_t encoded[16];
  size_t encodedLength = cobsEncode(rawData, sizeof(rawData), encoded);

  // Append COBS frame delimiter
  encoded[encodedLength++] = 0x00;

  // Transmit over Serial
  Serial.write(encoded, encodedLength);

  // Wait 100ms
  delay(100);
  t++;
}

Checklist

• I ran npm run lint and fixed any issues
• I ran npm run typecheck (TypeScript) with no errors
• I ran npm test and tests pass
• I ran npm run test:coverage if code paths changed significantly
• I added/updated tests where appropriate
• I updated docs/README if needed
• No breaking changes without clear migration notes

Additional Notes

GPT-5 was used to help write cobsDecoder.ts
handleIncomingLine (in src/App.tsx) ought to be refactored at some point to remove the hack I added on line 194 of src/hooks/userSerial.ts