Upgrade JVM toolchain to 25 and Kotlin toolchain to 2.3.20 (#1516)

Motivation
- Enable correct NullAway analysis
- Pick up toolchain fixes and improvements

Toolchains
- Require JDK 25 for JVM toolchain (keep Java 17 runtime compatibility)
- Require Kotlin 2.3.20 for Kotlin toolchain (keep Kotlin 2.2 runtime
compatibility)
- Require JDK 25 for Gradle daemon JVM (via
gradle-daemon-jvm.properties)
- Fix javac and kotlinc warnings from toolchain upgrades

CI
- Bump GitHub workflows to JDK 25

Building Kotlin
- Bump Kotlin language level to 2.2 to match stdlib version
- Consolidate build logic into pklKotlinBase.gradle.kts
- Adopt modern Kotlin plugin syntax
- Fix new kotlinc warnings
- Update ktfmt to 0.62
  - first version compatible with Kotlin 2.3.20
  - changes formatting compared to 0.61
- Replace dependency resolution rule with BOM alignment
  - rule was too broad and interfered with toolchain/runtime separation

Testing
- Expand matrix to JDK 25 (LTS) and 26
- Ensure each matrix task can be run independently
- Fix KotlinCodeGeneratorsTest and EmbeddedExecutorsTest on affected
JDKs
- Disable one test in CliCommandTest on affected JDKs (failure cause
unknown)

Compatibility fixes
- Fix reflective access in DocGenerator on affected JDKs

Build fixes
- Fix misuse of `task.enabled` vs. `report.required`
- Fix `gradlew tasks` on Windows
- Downgrade Spotless to 8.3.0 to (hopefully) work around sporadic
NoClassDefFoundError

Result
- NullAway runs correctly
- Broader JDK test coverage
- More reproducible and potentially faster builds

buildSrc/src/main/kotlin/pklJavaLibrary.gradle.kts

@@ -58,17 +58,8 @@ spotless {
     target("src/*/java/**/*.java")
     licenseHeaderFile(rootProject.file("buildSrc/src/main/resources/license-header.star-block.txt"))
   }
-
-  kotlin {
-    addStep(revertYearOnlyChanges)
-    ktfmt(libs.versions.ktfmt.get()).googleStyle()
-    target("src/*/kotlin/**/*.kt")
-    licenseHeaderFile(rootProject.file("buildSrc/src/main/resources/license-header.star-block.txt"))
-  }
 }
 
-tasks.compileKotlin { enabled = false }
-
 tasks.jar {
   manifest {
     attributes +=
@@ -86,19 +77,6 @@ tasks.javadoc {
   (options as StandardJavadocDocletOptions).addStringOption("Xdoclint:none", "-quiet")
 }
 
-val workAroundKotlinGradlePluginBug by
-  tasks.registering {
-    doLast {
-      // Works around this problem, which sporadically appears and disappears in different
-      // subprojects:
-      // A problem was found with the configuration of task ':pkl-executor:compileJava' (type
-      // 'JavaCompile').
-      // > Directory '[...]/pkl/pkl-executor/build/classes/kotlin/main'
-      // specified for property 'compileKotlinOutputClasses' does not exist.
-      layout.buildDirectory.dir("classes/kotlin/main").get().asFile.mkdirs()
-    }
-  }
-
 val truffleJavacArgs =
   listOf(
     // TODO: determine correct limits for Truffle specializations
@@ -108,7 +86,6 @@ val truffleJavacArgs =
 
 tasks.compileJava {
   javaCompiler = info.javaCompiler
-  dependsOn(workAroundKotlinGradlePluginBug)
   options.compilerArgs.addAll(truffleJavacArgs + info.jpmsAddModulesFlags)
 }