ipairs terminates on the first nil index when iterating over table keys:

for i,k in ipairs( {[1] = 'test', [3] = 'test'} ) do
  print(i, k)
end

prints:
1 test

Instead, use pairs which continues iterating over the entire table:

for i,k in pairs( {[1] = 'test', [3] = 'test'} ) do
  print(i, k)
end

prints:
1 test
3 test

- Fix the cursor position after applying TextEdits
- Support reversed range of TextEdit
- Invoke nvim_buf_set_text one by one

* Simplify rpc encode/decode messages to rpc.send/rcp.receive
* Make missing handlers message throw a warning
* Clean up formatting style in log
* Move all non-RPC loop messages to trace instead of debug
* Add format func option to log to allow newlines in per log entry

This fixes the handler signature and also prevents n+1 requests firing
if there are multiple clients.

(The first `prepareCallHierarchy` handler is called once per client,
each invocation used `buf_request` to make more requests using *all*
clients)

Follow up to https://github.com/neovim/neovim/pull/15504

`return err_message(tostring(err))` caused errors to be printed as
`table: 0x123456789` instead of showing the error code and error
message.

This also removes some `if err` blocks that never got called because at
the end of `handlers.lua` all the handlers are wrapped with logic that
adds generic error handling.

Relates to https://github.com/neovim/neovim/issues/15050

Users should get some indication if there was an error or an empty
result.