[core] add OffsetRange class (#10436)

This commit introduces the `OffsetRange` class, which represents a
range of offsets within a `Message` or data buffer (i.e., a starting
offset and a length indicating the number of bytes in the range).

The class provides methods for common operations:

- Getting the start or end offset, or the remaining length.
- Checking if the range is empty or contains a certain number of
  bytes.
- Advancing the start offset by a given amount, ensuring it never goes
  beyond the end offset.
- Shrinking the range's length.

The new `OffsetRange` class simplifies methods that previously used
separate `aOffset` and `aLength` input parameters, improving code
readability and maintainability. It also facilitates reading and
processing content within a specified range.

For example, `Tlv::FindTlvValueOffsetRange()` now directly returns an
`OffsetRange` indicating the location of the TLV value. The `Message`
class is also updated with new `Read()` and `Append()` method variants
that accept `OffsetRange` arguments. These methods ensure that read
content is contained within the specified `OffsetRange`.

tests/unit/test_lowpan.cpp

@@ -103,6 +103,7 @@ void TestIphcVector::GetUncompressedStream(Message &aMessage)
 static void Init(void)
 {
     otMeshLocalPrefix meshLocalPrefix = {{0xfd, 0x00, 0xca, 0xfe, 0xfa, 0xce, 0x12, 0x34}};
+    OffsetRange       offsetRange;
 
     sInstance->Get<Mle::MleRouter>().SetMeshLocalPrefix(static_cast<Ip6::NetworkPrefix &>(meshLocalPrefix));
 
@@ -127,8 +128,10 @@ static void Init(void)
 
     SuccessOrQuit(message->AppendBytes(mockNetworkData, sizeof(mockNetworkData)));
 
+    offsetRange.Init(2, 0x20);
+
     IgnoreError(
-        sInstance->Get<NetworkData::Leader>().SetNetworkData(0, 0, NetworkData::kStableSubset, *message, 2, 0x20));
+        sInstance->Get<NetworkData::Leader>().SetNetworkData(0, 0, NetworkData::kStableSubset, *message, offsetRange));
 }
 
 /**