fix(lsp): renderDiagnostic and explainError hash collisions

The list of positions we've visited so far was hashed as line number +
column number which meant that if a diagnostic was at line 9, column 16
it would conflict with one at line 21, column 4, for example. This would
result in diagnostics later in the file being skipped even if they were
closer to where the cursor was.

We now hash the list with 1000 * line number + column number so that a
conflict is only possible if a diagnostic is at column 1000 or more.
Conflicts are still technically possible, but this was faster to
implement than a full solution which would store the exact cursor
position for each diagnostic visited so far.

lua/rustaceanvim/commands/diagnostic.lua

@@ -102,7 +102,7 @@ function M.explain_error()
         break
       end
     end
-    pos_id = pos[1] + pos[2]
+    pos_id = pos[1] * 1000 + pos[2]
     -- diagnostics are (0,0)-indexed but cursors are (1,0)-indexed
     opts.cursor_position = { pos[1] + 1, pos[2] }
     local searched_all = pos_map[pos_id] ~= nil
@@ -203,7 +203,7 @@ function M.render_diagnostic()
         break
       end
     end
-    pos_id = pos[1] + pos[2]
+    pos_id = pos[1] * 1000 + pos[2]
     -- diagnostics are (0,0)-indexed but cursors are (1,0)-indexed
     opts.cursor_position = { pos[1] + 1, pos[2] }
     local searched_all = pos_map[pos_id] ~= nil