Add micro-benchmark for layer map search function

The test data was extracted from our pgbench benchmark project on the
captest environment, the one we use for the 'neon-captest-reuse' test.

Cargo.lock

@@ -2139,6 +2139,7 @@ dependencies = [
  "close_fds",
  "const_format",
  "crc32c",
+ "criterion",
  "crossbeam-utils",
  "daemonize",
  "etcd_broker",

pageserver/Cargo.toml

@@ -69,5 +69,10 @@ close_fds = "0.3.2"
 walkdir = "2.3.2"
 
 [dev-dependencies]
+criterion = "0.4"
 hex-literal = "0.3"
 tempfile = "3.2"
+
+[[bench]]
+name = "bench_layer_map"
+harness = false

pageserver/src/tenant.rs

@@ -59,13 +59,14 @@ pub mod block_io;
 mod delta_layer;
 mod disk_btree;
 pub(crate) mod ephemeral_file;
-mod filename;
+pub mod filename;
 mod image_layer;
 mod inmemory_layer;
-mod layer_map;
+pub mod layer_map;
+
 pub mod metadata;
 mod par_fsync;
-mod storage_layer;
+pub mod storage_layer;
 
 mod timeline;