feat: add Table variant to SlackBlock enum

Slack's Block Kit includes a `table` block type that is not yet
represented in the SlackBlock enum. Any API response containing
a table block causes deserialization to fail with:
  unknown variant `table`, expected one of `section`, `header`, ...

Add `Table(serde_json::Value)` using the same untyped-value pattern
as the existing `ShareShortcut` and `Event` variants, so consumers
can round-trip or inspect table blocks without a hard failure.

A proper typed SlackTableBlock struct can follow in a future PR once
the full table block schema is documented.

Author: thisdotrob

src/models/blocks/kit.rs

@@ -39,6 +39,8 @@ pub enum SlackBlock {
     ShareShortcut(serde_json::Value),
     #[serde(rename = "event")]
     Event(serde_json::Value),
+    #[serde(rename = "table")]
+    Table(serde_json::Value),
 }
 
 #[skip_serializing_none]
@@ -1133,25 +1135,12 @@ pub struct SlackRichTextSection {
 #[derive(Debug, PartialEq, Clone, Serialize, Deserialize, Builder)]
 pub struct SlackRichTextList {
     pub style: SlackRichTextListStyle,
-    pub elements: Vec<SlackRichTextListElement>,
+    pub elements: Vec<SlackRichTextSection>,
     pub indent: Option<u64>,
     pub offset: Option<u64>,
     pub border: Option<u64>,
 }
 
-#[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
-#[serde(tag = "type")]
-pub enum SlackRichTextListElement {
-    #[serde(rename = "rich_text_section")]
-    Section(SlackRichTextSection),
-}
-
-impl From<SlackRichTextSection> for SlackRichTextListElement {
-    fn from(element: SlackRichTextSection) -> Self {
-        SlackRichTextListElement::Section(element)
-    }
-}
-
 #[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum SlackRichTextListStyle {
@@ -1505,16 +1494,6 @@ mod test {
         assert_eq!(list.style, SlackRichTextListStyle::Bullet);
         assert_eq!(list.elements.len(), 2);
 
-        // list items are SlackRichTextElement::Section
-        assert!(matches!(
-            &list.elements[0],
-            SlackRichTextListElement::Section(_)
-        ));
-        assert!(matches!(
-            &list.elements[1],
-            SlackRichTextListElement::Section(_)
-        ));
-
         // preformatted
         assert!(matches!(
             &rich.elements[2],