Summary

Add support for "3-latest.candidate" to automatically resolve to the latest Scala 3 RC from Maven Central.

scalaVersion := "3-latest.candidate"

Ref #8590

Changes

• Add scalaDynVersion task that resolves dynamic version strings
• Fetch and parse Maven Central metadata to find the latest RC (pattern: X.Y.Z-RCN, excludes nightlies)
• Cache results for 24 hours across all subprojects
• Handle dynamic patterns in binaryScalaVersion, earlyScalaVersion, and isScala3

Test plan

• Unit tests for version utility functions
• Scripted test verifying resolution and compilation

Fixes #8595