feature: implement undocumented R2 startAfter API

This adds the `startAfter` list option which is implemented,
however undocumented. This is equivalent to the `marker` field
in the s3 api.

Author: fisherdarling

worker/src/r2/builder.rs

@@ -379,6 +379,7 @@ pub struct ListOptionsBuilder<'bucket> {
     pub(crate) edge_bucket: &'bucket EdgeR2Bucket,
     pub(crate) limit: Option<u32>,
     pub(crate) prefix: Option<String>,
+    pub(crate) start_after: Option<String>,
     pub(crate) cursor: Option<String>,
     pub(crate) delimiter: Option<String>,
     pub(crate) include: Option<Vec<Include>>,
@@ -397,6 +398,12 @@ impl ListOptionsBuilder<'_> {
         self
     }
 
+    /// Start listing after this key.
+    pub fn start_after(mut self, start_after: impl Into<String>) -> Self {
+        self.start_after = Some(start_after.into());
+        self
+    }
+
     /// An opaque token that indicates where to continue listing objects from. A cursor can be
     /// retrieved from a previous list operation.
     pub fn cursor(mut self, cursor: impl Into<String>) -> Self {
@@ -437,6 +444,7 @@ impl ListOptionsBuilder<'_> {
             js_object! {
                 "limit" => self.limit,
                 "prefix" => self.prefix,
+                "startAfter" => self.start_after.map(JsValue::from),
                 "cursor" => self.cursor,
                 "delimiter" => self.delimiter,
                 "include" => self

worker/src/r2/mod.rs

@@ -104,6 +104,7 @@ impl Bucket {
             edge_bucket: &self.inner,
             limit: None,
             prefix: None,
+            start_after: None,
             cursor: None,
             delimiter: None,
             include: None,