fix: pass client.offset_encoding to make_position_params (#1)

[ppmzhang2]

This fixes a warning emitted by Neovim when invoking vim.lsp.util.make_position_params() without specifying a position_encoding. Previously, the plugin always fell back to the default encoding, producing the message:

position_encoding param is required in vim.lsp.util.make_position_params. Defaulting to position encoding of the first client.

To fix it, we pass client.offset_encoding to make_position_params in M.request_inline_completion to remove the noisy warning and ensure correct position encoding is used.