Adjust morning-session timings downward (#1786)

Based on feedback from @marshallpierce that mornings took about 2.5
hours, this adjusts a bunch of the morning times downward to try to
match that. In other words, this is trying to make the times in the
course more accurate, rather than reducing the amount of time available
for these slides.

This also updates the `course-schedule` tool to be able to show
per-segment timings.

src/testing/lints.md

@@ -1,5 +1,5 @@
 ---
-minutes: 5
+minutes: 3
 ---
 
 # Compiler Lints and Clippy

src/testing/other.md

@@ -1,5 +1,5 @@
 ---
-minutes: 10
+minutes: 5
 ---
 
 # Other Types of Tests

src/testing/unit-tests.md

@@ -23,7 +23,7 @@ fn first_word(text: &str) -> &str {
 }
 
 #[cfg(test)]
-mod test {
+mod tests {
     use super::*;
 
     #[test]