SIMD-0391: Feature-gate fixed-point stake math

[grod220]

Problem

The current stake warmup/cooldown calculations use floating-point arithmetic which blocks the stake program from being compatible with the upstream bpf toolchain. SIMD-0391 specifies a transition to fixed-point integer math which is implemented in the solana-stake-interface crate. In this PR, these exposed methods are feature gated. All validator clients and the stake program itself will need to be updated in lock step.

Summary of Changes

• Add new feature gate stake_program_fixed_point_warmup_cooldown
• Introduce runtime dispatch helpers to select legacy float vs fixed-point stake math based on the feature gate. Updates are present in:
  • stake cache updates and vote delegated stake aggregation
  • epoch cache refresh
  • inflation rewards points calculation and reward redemption
• Added parameterized testings for legacy/fixed point methods

Rollout plan

• SIMD-0391 approved and merged (waiting on this)
• Convert warmup/cooldown rates to integers solana-program/stake#152 approved and merged (interface helpers + stake program integration)
• Firedancer support, part 1: Float-to-fixed point stake calculations firedancer-io/firedancer#7589. Part 2 is feature gating.
• Agave support: this PR

Feature Gate Issue: #