Feat/messages api (#546)

* fix test server setup:
- go map access is not deterministic
- this can lead to a route: /foo/bar/1 matching /foo/bar before matching /foo/bar/1 if the map iteration go through /foo/bar first since the regex match wasn't bound to start and end anchors
- registering handlers now converts * in routes to .* for proper regex matching
- test server route handling now tries to fully match the handler route

* add missing /v1 prefix to fine-tuning job cancel test server handler

* add create message call

* add messages list call

* add get message call

* add modify message call, fix return types for other message calls

* add message file retrieve call

* add list message files call

* code style fixes

* add test for list messages with pagination options

* add beta header to msg calls now that #545 is merged

* Update messages.go

Co-authored-by: Simone Vellei <henomis@gmail.com>

* Update messages.go

Co-authored-by: Simone Vellei <henomis@gmail.com>

* add missing object details for message, fix tests

* fix merge formatting

* minor style fixes

---------

Co-authored-by: Simone Vellei <henomis@gmail.com>

client_test.go

@@ -301,6 +301,24 @@ func TestClientReturnsRequestBuilderErrors(t *testing.T) {
 		{"DeleteAssistantFile", func() (any, error) {
 			return nil, client.DeleteAssistantFile(ctx, "", "")
 		}},
+		{"CreateMessage", func() (any, error) {
+			return client.CreateMessage(ctx, "", MessageRequest{})
+		}},
+		{"ListMessage", func() (any, error) {
+			return client.ListMessage(ctx, "", nil, nil, nil, nil)
+		}},
+		{"RetrieveMessage", func() (any, error) {
+			return client.RetrieveMessage(ctx, "", "")
+		}},
+		{"ModifyMessage", func() (any, error) {
+			return client.ModifyMessage(ctx, "", "", nil)
+		}},
+		{"RetrieveMessageFile", func() (any, error) {
+			return client.RetrieveMessageFile(ctx, "", "", "")
+		}},
+		{"ListMessageFiles", func() (any, error) {
+			return client.ListMessageFiles(ctx, "", "")
+		}},
 		{"CreateThread", func() (any, error) {
 			return client.CreateThread(ctx, ThreadRequest{})
 		}},