cache base_reward_per_increment for 5x+ Altair block_sim perf increase

[tersec]

Before:

Validators: 60000, epoch length: 32
Validators per attestation (mean): 0.0
All time are ms
     Average,       StdDev,          Min,          Max,      Samples,         Test
     851.181,      824.055,       36.696,     2495.847,          186, Process non-epoch slot with block
    1790.548,     1320.587,       90.843,     2892.819,            6, Process epoch slot with block
       0.140,        0.015,        0.012,        0.188,          192, Tree-hash block
       0.514,        0.037,        0.386,        0.692,          192, Sign block
     800.085,       17.178,      748.724,      854.023,          192, Have committee attest to block
      55.202,        0.000,       55.202,       55.202,            1, Replay all produced blocks

After:

Validators: 60000, epoch length: 32
Validators per attestation (mean): 0.0
All time are ms
     Average,       StdDev,          Min,          Max,      Samples,         Test
      69.611,       41.232,       51.829,      608.034,          186, Process non-epoch slot with block
     663.736,      420.768,      129.060,     1020.310,            6, Process epoch slot with block
       0.141,        0.011,        0.012,        0.174,          192, Tree-hash block
       0.518,        0.020,        0.474,        0.632,          192, Sign block
     846.612,       18.642,      815.442,      933.857,          192, Have committee attest to block
      58.445,        0.000,       58.445,       58.445,            1, Replay all produced blocks

real	3m3.258s
user	2m58.386s
sys	0m2.212s

The first three epochs aren't changed, so the Altair-specific changes are more than the averages shown.

[github-actions]

Unit Test Results

     28 files  ±0     328 suites  ±0   1h 3m 44s ⏱️ ±0s
   631 tests ±0     613 ✔️ ±0    18 💤 ±0  0 ❌ ±0 
3 452 runs  ±0  3 348 ✔️ ±0  104 💤 ±0  0 ❌ ±0 

Results for commit 60f601e. ± Comparison against base commit 60f601e.

♻️ This comment has been updated with latest results.