chore: Migrate from bloop-frontend to scala-cli for compilation

[oyvindberg]

Summary

Replace bloop-frontend with scala-cli for compiling generated Scala.js code, enabling cross-compilation to Scala 3.

Motivation

We need to cross-compile the converter to Scala 3, but we're facing dependency issues:

• Historical context: We used bloop-frontend for historical reasons as a lightweight compilation solution
• Scala 3 blocker: bloop-frontend doesn't exist for Scala 3
• Bloop-rifle alternative: While bloop-rifle exists for Scala 3, it doesn't support Scala 2.12
• Solution: Migrate to scala-cli which is called through command line

Benefits

1. Cross-compilation ready: Enables the converter to work with Scala 3
2. Dramatically simpler dependency graph: Removes complex bloop dependencies
3. Better maintained: scala-cli is actively developed and well-supported
4. Consistent tooling: Uses a modern, standard tool in the Scala ecosystem

Important Note

This change does NOT affect the SBT plugin, which continues to use the Scala compiler through SBT's own infrastructure.

Changes

• Removed BloopCompiler.scala and its dependencies
• Added ScalaCliCompiler.scala with equivalent functionality
• Downloads scala-cli binary automatically for the target platform
• Generates build directives for scala-cli instead of bloop config
• Added comprehensive tests for different OS/arch combinations

Implementation Details

The ScalaCliCompiler:

• Downloads the appropriate scala-cli binary for the current platform
• Generates a temporary build.scala file with scala-cli directives
• Compiles the generated Scala.js code using scala-cli's built-in compilation
• Properly handles dependencies through classpath configuration
• Provides improved logging with pattern matching on output levels

Testing

Added tests covering:

• Binary download for all supported platforms (macOS, Linux, Windows)
• Architecture normalization (amd64 → x86_64, arm64 → aarch64)
• Executable permission verification
• Binary format validation

Migration Path

This is a drop-in replacement - no changes required to existing code using the compiler interface.