Auto merge of #75752 - jakoschiko:test-suite-time, r=m-ou-se

libtest: Print the total time taken to execute a test suite

Print the total time taken to execute a test suite by default, without any kind of flag.

Closes #75660

# Example
```
anon@anon:~/code/rust/example$ cargo test
   Compiling example v0.1.0 (/home/anon/code/rust/example)
    Finished test [unoptimized + debuginfo] target(s) in 0.18s
     Running target/debug/deps/example-745b64d3885c3565

running 3 tests
test tests::foo ... ok
test tests::bar ... ok
test tests::baz ... ok

test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; 1.2s

   Doc-tests example

running 3 tests
test src/lib.rs - foo (line 3) ... ok
test src/lib.rs - bar (line 11) ... ok
test src/lib.rs - baz (line 19) ... ok

test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; 1.3s
```

```
anon@anon:~/code/rust/example$ cargo test -- --format terse
    Finished test [unoptimized + debuginfo] target(s) in 0.08s
     Running target/debug/deps/example-745b64d3885c3565

running 3 tests
...
test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; 1.2s

   Doc-tests example

running 3 tests
...
test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; 1.3s
```

```
anon@anon:~/code/rust/example$ cargo test -- --format json -Z unstable-options
   Compiling example v0.1.0 (/home/anon/code/rust/example)
    Finished test [unoptimized + debuginfo] target(s) in 0.25s
     Running target/debug/deps/example-745b64d3885c3565
{ "type": "suite", "event": "started", "test_count": 3 }
{ "type": "test", "event": "started", "name": "tests::bar" }
{ "type": "test", "event": "started", "name": "tests::baz" }
{ "type": "test", "event": "started", "name": "tests::foo" }
{ "type": "test", "name": "tests::foo", "event": "ok" }
{ "type": "test", "name": "tests::bar", "event": "ok" }
{ "type": "test", "name": "tests::baz", "event": "ok" }
{ "type": "suite", "event": "ok", "passed": 3, "failed": 0, "allowed_fail": 0, "ignored": 0, "measured": 0, "filtered_out": 0, "exec_time": "1.2s" }
   Doc-tests example
{ "type": "suite", "event": "started", "test_count": 3 }
{ "type": "test", "event": "started", "name": "src/lib.rs - bar (line 11)" }
{ "type": "test", "event": "started", "name": "src/lib.rs - baz (line 19)" }
{ "type": "test", "event": "started", "name": "src/lib.rs - foo (line 3)" }
{ "type": "test", "name": "src/lib.rs - foo (line 3)", "event": "ok" }
{ "type": "test", "name": "src/lib.rs - bar (line 11)", "event": "ok" }
{ "type": "test", "name": "src/lib.rs - baz (line 19)", "event": "ok" }
{ "type": "suite", "event": "ok", "passed": 3, "failed": 0, "allowed_fail": 0, "ignored": 0, "measured": 0, "filtered_out": 0, "exec_time": "1.3s" }
```

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