Update Concurrency course with times (#2007)

As I mentioned in #1536:

* Break into segments at approximately the places @fw-immunant put
breaks
 * Move all of the files into `src/concurrency`
 * Add timings and segment/session metadata so course outlines appear

There's room for more work here, including some additional feedback from
@fw-immunant after the session I observed, but let's do one step at a
time :)

Cargo.lock

@@ -322,16 +322,6 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "acbf1af155f9b9ef647e42cdc158db4b64a1b61f743629225fde6f3e0be2a7c7"
 
-[[package]]
-name = "comprehensive-rust"
-version = "0.1.0"
-dependencies = [
- "reqwest",
- "scraper",
- "tempfile",
- "thiserror",
-]
-
 [[package]]
 name = "control-flow-basics"
 version = "0.1.0"
@@ -2412,6 +2402,16 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "sync-exercises"
+version = "0.1.0"
+dependencies = [
+ "reqwest",
+ "scraper",
+ "tempfile",
+ "thiserror",
+]
+
 [[package]]
 name = "sync_wrapper"
 version = "0.1.2"