feat: ignore messages via to filter functions

Previously, messages could only be ignored according to the name of the
LSP server they come from. (Prior to the legacy rewrite, this feature
was part of the user-specified render function. Kind of ugly how that
worked.)

This feature allows messages to be ignored according to logic in
arbitrary user-specified functions.

The slightly yucky thing about this design is that the "shape" of the
message object is not really well-specified or documented. For example,
it is not obvious why we need to check `msg.title` rather than anything
else. The example should be good enough though, at least for now.

Addresses #249

lua/fidget/progress.lua

@@ -100,14 +100,28 @@ progress.options   = {
     return client and client.name or nil
   end,
 
-  --- List of LSP servers to ignore
+  --- List of filters to ignore LSP progress messages
+  ---
+  --- Each filter is either a string or a function.
+  ---
+  --- If it is a string, then it is treated as the name of a LSP server;
+  --- messages from that server are ignored.
+  ---
+  --- If it is a function, then the progress message object is passed to the
+  --- function. If the function returns a truthy value, then that message is
+  --- ignored.
   ---
   --- Example:
   --->lua
-  ---     ignore = { "rust_analyzer" }
+  ---     ignore = {
+  ---       "rust_analyzer",  -- Ignore all messages from rust-analyzer
+  ---       function(msg)     -- Ignore messages containing "ing"
+  ---         return string.find(msg.title, "ing") ~= nil
+  ---       end,
+  ---     }
   ---<
   ---
-  ---@type Key[]
+  ---@type (string|fun(msg: ProgressMessage): any)[]
   ignore = {},
 
   display = progress.display,
@@ -214,13 +228,21 @@ progress.poller = poll.Poller {
     for _, msg in ipairs(messages) do
       -- Determine if we should ignore this message
       local ignore = false
-      for _, lsp_name in ipairs(progress.options.ignore) do
-        -- NOTE: hopefully this loop isn't too expensive.
-        -- But if it is, consider indexing by hash.
-        if msg.lsp_client.name == lsp_name then
-          ignore = true
-          logger.info("Ignoring LSP progress message from", lsp_name, ":", msg)
-          break
+      for _, filter in ipairs(progress.options.ignore) do
+        if type(filter) == "string" then
+          if msg.lsp_client.name == filter then
+            ignore = true
+            logger.info("Ignoring LSP progress message by name from", filter, ":", msg)
+            break
+          end
+        elseif type(filter) == "function" then
+          if filter(msg) then
+            ignore = true
+            logger.info("Filtering out LSP progress message", ":", msg)
+            break
+          end
+        else
+          logger.error("Unsupported filter type:", type(filter))
         end
       end
       if not ignore then