[build] fix non-dev plugin version setting

[pq]

Fixes borked version setting for non-dev builds.

☁  third_party [build_fixProdVersion] ⚡  ./gradlew buildPlugin -Pdev
Calculating task graph as configuration cache cannot be reused because the set of Gradle properties has changed: 'dev' was added.

> Configure project :
plugin version: 504.0.0-dev.20260331
ideaVersion: 251 to 261.*
DART_HOME environment variable is not set. Dart Analysis Server tests will fail.
Following 1 plugins could not be created: plugins/fullLine/lib/modules/intellij.fullLine.yaml.jar

BUILD SUCCESSFUL in 4s
15 actionable tasks: 8 executed, 3 from cache, 4 up-to-date
Configuration cache entry stored.

☁  third_party [build_fixProdVersion] ⚡  ./gradlew buildPlugin      
Calculating task graph as configuration cache cannot be reused because the set of Gradle properties has changed: 'dev' was removed.

> Configure project :
plugin version: 503.0.0
ideaVersion: 251 to 261.*
DART_HOME environment variable is not set. Dart Analysis Server tests will fail.
Following 1 plugins could not be created: plugins/fullLine/lib/modules/intellij.fullLine.yaml.jar

BUILD SUCCESSFUL in 4s
15 actionable tasks: 8 executed, 3 from cache, 4 up-to-date
Configuration cache entry stored.

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[gemini-code-assist]

Code Review

This pull request refactors the plugin versioning logic in build.gradle.kts to handle development builds more explicitly and updates the logging of version information. Feedback was provided to improve the idiomatic use of Kotlin by preferring immutable variables and conditional assignments for the version calculation logic.

[pq]

(This is a bit more idiomatic.)

[pq]

These printlns were not working as expected.