fix(helix-dap): seq number must start at 1

[likle]

Hi there, this is a bit outside of my expertise but I had some issues running the debugger for C projects, due to the following error: helix_dap::transport [ERROR] err <- DAP session error: expected to not be '0' at (root).seq
The user only sees Failed to start debug client: server closed the stream

it seems like lldb-dap is checking that the sequence number is non-zero:
https://github.com/llvm/llvm-project/blob/main/lldb/tools/lldb-dap/Protocol/ProtocolBase.cpp#L96

The DAP specification says this:

The seq for the first message sent by a client or debug adapter is 1

This made me assume that the lldb-dap check is probably correct. In this pull request I added an increment instead of setting the initial value of the request_counter to 1 in order to maintain the semantic meaning of the variable. This change has only been tested with lldb v21.1.3 with C on linux (arch).

[the-mikedavis]

Well spotted, thanks! I pushed a change just to add a comment linking to the relevant doc