Fix descriptor search range in retrieveDescriptors()

[syscode1]

Problem

The NimBLERemoteCharacteristic::retrieveDescriptors() function incorrectly uses the service's end handle (getRemoteService()->getEndHandle()) as the search range limit when discovering descriptors.

This causes the following bug:

• Descriptors from subsequent characteristics within the same service are incorrectly included
• Results in wrong descriptors being associated with the current characteristic
• Causes memory waste and logical errors

Example scenario:

Service (Handle 0x0001 - 0x0010)
  ├─ Characteristic A (Handle 0x0002)
  │   ├─ Descriptor A1 (Handle 0x0003)
  │   └─ Descriptor A2 (Handle 0x0004)
  ├─ Characteristic B (Handle 0x0005)
  │   └─ Descriptor B1 (Handle 0x0006)

Before fix: Searching descriptors for Characteristic A returns A1, A2, and B1 ❌
After fix: Searching descriptors for Characteristic A returns only A1 and A2 ✅

Solution

This PR fixes the issue by:

1. Finding the next characteristic in the service
2. Using next_characteristic_handle - 1 as the end handle for descriptor search
3. Ensuring only descriptors belonging to the current characteristic are retrieved
4. Maintaining backward compatibility for the last characteristic in a service

Changes Made

• Modified retrieveDescriptors() to iterate through service characteristics
• Calculate correct endHandle based on the next characteristic's handle
• Falls back to service end handle for the last characteristic
• Added debug logging for the calculated search range

Testing

This fix correctly handles:

• ✅ Services with multiple characteristics
• ✅ Last characteristic in a service
• ✅ Characteristics with no descriptors

Files Changed

• src/NimBLERemoteCharacteristic.cpp (+18 lines, -2 lines)

[h2zero]

Thanks! Looks like I broke this in 2.0.0 and hasn't been noticed until now. Could you please rebase this so only the changes required are in the PR?