perf(storage): converge Wave 2 hot-path optimizations (#6065)

* perf(get): share inline shards and lock clients

Co-Authored-By: heihutu <heihutu@gmail.com>

* perf(ecstore): converge PUT encoding on contiguous blocks

Co-Authored-By: heihutu <heihutu@gmail.com>

* perf(get): cache codec streaming gate config

Co-Authored-By: heihutu <heihutu@gmail.com>

* fix(sse): redact projected customer headers

Co-Authored-By: heihutu <heihutu@gmail.com>

* perf(ecstore): collapse GET metadata snapshots

Co-Authored-By: heihutu <heihutu@gmail.com>

* perf(ecstore): reuse decode stripe scratch

Co-Authored-By: heihutu <heihutu@gmail.com>

* refactor(ecstore): trim decode scratch adapters

Co-Authored-By: heihutu <heihutu@gmail.com>

* test(ecstore): adapt transition checks to metadata snapshots

Co-Authored-By: heihutu <heihutu@gmail.com>

* perf(get): release metadata snapshots at ownership boundary

Co-Authored-By: heihutu <heihutu@gmail.com>

* refactor(ecstore): close cumulative fast-path findings

Co-Authored-By: heihutu <heihutu@gmail.com>

* fix(storage): preserve lock and header invariants

Co-Authored-By: heihutu <heihutu@gmail.com>

* test(ecstore): adapt cumulative paths after rebase

Co-Authored-By: heihutu <heihutu@gmail.com>

* fix(rio-v2): adapt generated metadata fixture

Co-Authored-By: heihutu <heihutu@gmail.com>

---------

Co-authored-by: heihutu <heihutu@gmail.com>

crates/ecstore/src/erasure/codec/workspace.rs

@@ -76,6 +76,13 @@ impl ShardBufferPool {
         self.buffers[index] = Some(buf);
     }
 
+    #[cfg(test)]
+    pub(crate) fn stored_allocation(&self, index: usize) -> Option<(*const u8, usize)> {
+        self.buffers
+            .get(index)
+            .and_then(|buf| buf.as_ref().map(|buf| (buf.as_ptr(), buf.capacity())))
+    }
+
     #[cfg(test)]
     fn stored_capacity(&self, index: usize) -> Option<usize> {
         self.buffers.get(index).and_then(|buf| buf.as_ref().map(Vec::capacity))