Artefacts upload update

[suu-yi]

Architecture

• Artifact build moved from CyteTypeR() to PrepareCyteTypeR() — vars.h5 and obs.duckdb are now built during prep, not submission
• CleanUpArtifacts() added — new exported function to remove artifact files after a run

Artifacts (artifacts.R)

• Raw counts group added — raw/ CSR sparse group written to vars.h5 alongside vars/ CSC group
• raw/data dtype fixed — int32 (matching Python spec) instead of float32
• source_name / source_dtype attributes added to info/var/columns/* datasets

Client & API

• Upload timeout increased
• Max file size increased
• Error handling improvements in errors.R and error catching in build/upload flow

Seurat helpers

• droplevels() on metadata — unused factor levels dropped before aggregation
• Full coordinates — visualization data now passes complete coordinates
• Schema updated — additional validation in schema.R

Docs & meta

• Version bumped to 0.4.0
• NAMESPACE updated for new exports
• README — updated report links and images