This commit adds the core infrastructure for dependency lock files that
can skip Coursier resolution when a valid lock file exists, as specified
in issue sbt#2989.

New files in lm-coursier:
- LockFileData.scala: Data model for lock file (DependencyLock, ConfigurationLock, etc.)
- LockFileFormats.scala: JSON serialization using sjson-new
- LockFile.scala: Read/write utilities for lock files
- BuildClock.scala: SHA-1 computation for dependency validation
- ResolutionSerializer.scala: Extract/reconstruct Resolution from lock data
- LockFileSpec.scala: Unit tests for lock file serialization

Modified:
- ResolutionRun.scala: Added resolutionsWithLockFile() method

The key feature is the ability to reconstruct Coursier Resolution objects
from lock file data, enabling resolution skipping when the lock file is
valid (build clock matches).

…skipping

- Add lockFile field to CoursierConfiguration (with @SInCE for binary compat)
- Modify CoursierDependencyResolution.update to use resolutionsWithLockFile
- When lock file is valid, skip resolution and use cached data
- When lock file is missing/stale, perform resolution and write new lock file
- Update syntax/package.scala to include lockFile parameter

- Add ArtifactLock case class to store artifact URLs for direct fetching
- Update DependencyLock to include artifacts field
- Add JSON codec for ArtifactLock
- Fix BuildClock to include exclusions and strict settings for deterministic hashing
- Sort forceVersion entries for deterministic hash computation
- Update ResolutionSerializer.extractLockFileData to accept artifact map
- Update CoursierDependencyResolution to pass artifact URLs to lock file
- Update tests for new artifacts field

These fixes ensure the lock file contains enough information for
artifact fetching without requiring full resolution.

- Add LockedArtifactsRun to fetch artifacts directly from lock file URLs
- Add resolutionsWithLockFileData method to return lock file data for artifact fetching
- Modify CoursierDependencyResolution to use locked artifacts when lock file is valid
- Fallback to normal artifact fetching if locked artifact fetch fails

When a valid lock file exists, both resolution AND artifact discovery are
skipped - artifacts are fetched directly from the stored URLs. This provides
the full performance benefit of resolution skipping.

- Add lockFile parameter to LMCoursier.coursierConfiguration method
- Pass useDependencyLock and dependencyLockFile settings to CoursierConfiguration
- When useDependencyLock is true, the lock file path is passed to Coursier
- For sbt classifier and compiler bridge tasks, pass None (no lock file)

Test verifies that:
- Lock file is created on first update
- Subsequent updates use the lock file for resolution skipping
- Compile works with locked dependencies

- Pass silently if lock file doesn't exist
- Pass silently if lock file is valid
- Only throw exception if lock file exists but is stale

- Rename lock file check from build.sbt.lock to deps.lock
- Remove dependencyLockUpdate usage (use dependencyLock instead)
- dependencyLockCheck passes silently if no lock file or valid
- dependencyLockCheck throws exception only if lock file is stale