replay: make scheduler depth configurable

[ripatel-fd]

Make replay dispatcher depth configurable to save memory.
fd_rdisp_new takes a considerable amount of time with MSan (30s)
with the previous default.

Decreases live client depth to 1M and backtest depth to 8K.

[github-actions]

Performance Measurements ⏳

Suite	Baseline	New	Change
backtest mainnet-368528500-perf per slot	0.052089 s	0.052299 s	0.403% ✅
backtest mainnet-368528500-perf snapshot load	2.574 s	1.775 s	-31.041% ✅
backtest mainnet-368528500-perf total elapsed	52.088845 s	52.29853 s	0.403% ✅
firedancer mem usage with mainnet.toml	1003.33 GiB	971.33 GiB	-3.189% ✅

[github-actions]

Performance Measurements ⏳

Suite	Baseline	New	Change
backtest mainnet-368528500-perf per slot	0.052311 s	0.051958 s	-0.675% ✅
backtest mainnet-368528500-perf snapshot load	2.608 s	1.796 s	-31.135% ✅
backtest mainnet-368528500-perf total elapsed	52.310939 s	51.958081 s	-0.675% ✅
firedancer mem usage with mainnet.toml	1003.33 GiB	959.33 GiB	-4.385% ✅

[yufeng-jump]

lgtm overall just a few nits

[github-actions]

Performance Measurements ⏳

Suite	Baseline	New	Change
backtest mainnet-368528500-perf per slot	0.051966 s	0.052141 s	0.337% ✅
backtest mainnet-368528500-perf snapshot load	2.588 s	1.818 s	-29.753% ✅
backtest mainnet-368528500-perf total elapsed	51.9657 s	52.141432 s	0.338% ✅
firedancer mem usage with mainnet.toml	1003.33 GiB	987.33 GiB	-1.595% ✅

[github-actions]

Performance Measurements ⏳

Suite	Baseline	New	Change
backtest mainnet-368528500-perf per slot	0.052248 s	0.052223 s	-0.048% ✅
backtest mainnet-368528500-perf snapshot load	2.682 s	1.828 s	-31.842% ✅
backtest mainnet-368528500-perf total elapsed	52.248166 s	52.222542 s	-0.049% ✅
firedancer mem usage with mainnet.toml	1003.33 GiB	987.33 GiB	-1.595% ✅