Improve testing with stats and errors per test section

* TestRunner: separated the running of each "section" of a test into its own
  try-catch so that we can evaluate each section separately even if
  another section failed (e.g. evaluate all examples even if one test in
  "facts" throws an exception). I've added tests that exercise this "new
  feature".

* TestResults: refactored it a bit so that TestResults now has the three
  sections and the old TestResults becomes TestSectionResults. Also,
  TestSectionResults now has only *one* error, since that's what we get
  when there's an exception evaluating the Pkl code.

* SimpleReport:
  * Separated reporting of each test section so that it's easy to see
    which facts or which examples fail.

  * Added a "stats line" to the module and section levels that reports
    how many tests / assertions pass/fail. Note that, when reporting
    errors, there's no stats for the section since the error is all the
    info we get. Similarly, when examples fail, there's no stats because
    each example is converted into its own test so there are no
    failed assertions to report, it's all-or-nothing.

  * For the examples converted to tests, when multiple examples share
    the same name I've also added a counter ("# 1" and so on) so that
    it's easier to identify which one is failing.

* JUnitReport: fixed the reporting of failures as it wasn't consistent
  with "tests": the tests were the number of tests that we run but
  "failures" were the number of assertions that failed.

pkl-cli/src/test/kotlin/org/pkl/cli/CliTestRunnerTest.kt

@@ -62,8 +62,9 @@ class CliTestRunnerTest {
     assertThat(out.toString().stripFileAndLines(tempDir))
       .isEqualTo(
         """
-      module test
-        succeed ✅
+      module test ✅ 100.0% pass [1 passed]
+        facts ✅ 100.0% pass [1 passed]
+          succeed ✅ 100.0% pass [2 passed]
       
     """
           .trimIndent()
@@ -80,7 +81,7 @@ class CliTestRunnerTest {
       facts {
         ["fail"] {
           4 == 9
-          "foo" == "bar"
+          "foo" != "bar"
         }
       }
     """
@@ -96,10 +97,10 @@ class CliTestRunnerTest {
     assertThat(out.toString().stripFileAndLines(tempDir))
       .isEqualTo(
         """
-      module test
-        fail ❌
-          4 == 9 ❌
-          "foo" == "bar" ❌
+      module test ❌ 0.0% pass [0 passed, 1 failed]
+        facts ❌ 0.0% pass [0 passed, 1 failed]
+          fail ❌ 50.0% pass [1 passed, 1 failed]
+            4 == 9 ❌
       
     """
           .trimIndent()
@@ -118,7 +119,8 @@ class CliTestRunnerTest {
           9 == trace(9)
           "foo" == "foo"
         }
-        ["fail"] {
+        ["bar"] {
+          "foo" == "foo"
           5 == 9
         }
       }
@@ -136,8 +138,8 @@ class CliTestRunnerTest {
         """
       <?xml version="1.0" encoding="UTF-8"?>
       <testsuite name="test" tests="2" failures="1">
-          <testcase classname="test" name="foo"></testcase>
-          <testcase classname="test" name="fail">
+          <testcase classname="test.facts" name="foo"></testcase>
+          <testcase classname="test.facts" name="bar">
               <failure message="Fact Failure">5 == 9 ❌</failure>
           </testcase>
           <system-err><![CDATA[9 = 9