Export GFQL algorithm policy constants

[lmeyerov]

Summary

Expose shared constants for GFQL algorithm categories and tier restrictions so Graphistry server policy code can import them directly instead of maintaining duplicate string literals.

Context

• Graphistry server PR 2862 introduces policy enforcement that replicates GFQL algorithm categorizations and restriction sets.
• Review feedback asks to source these from PyGraphistry to avoid drift (code comments r2442784789 & r2442785165).

Desired Outcome

• Provide a PyGraphistry module that exports:
  • GFQL algorithm category metadata (for example mapping to LINEAR / ITERATIVE_GPU).
  • Tier-specific blocked/limited algorithm sets.
• Ensure the exports stay typed (Literal / Enum) to help downstream static checks.

Next Steps

• Decide the package location and public API (for example graphistry.compute.gfql.policy).
• Coordinate with the server repository to swap to the shared exports once available.