treewide: Add Spyglass flow and fix reported violations

[colluca]

Merge after #312.

• Add Spyglass lint flow and bump nonfree repo
• Fix all Spyglass lint errors and warnings
  • Remove redundant $signed conversions
  • Protect against negative array bounds when using default parameter values
  • Derive dependent type parameters
• Fix bug in hive's PTW request connections
• Bump OSEDA version to 2026.02 to include Verilator fix Fix nested struct in parameter port list (#6818) verilator/verilator#6824
• Add nonfree pysynthutils Python package dependency
• Add Spyglass lint checks (based on pysynthutils) to Gitlab CI
• Increase Yosys synthesis timeout to 3h in Gitlab CI
• Make snitch_cluster_pkg.sv a required source of the cluster, no longer required only by the cluster wrapper and test harness