fix(multi): skip unnecessary RPC calls in --cache mode

[fakedev9999]

Summary

• When --cache is used with explicit --start and --end, adds a fast path that skips all heavy RPC calls (optimism_rollupConfig, block range validation, host initialization)
• Prevents HTTP 403 errors on restricted RPC endpoints when running SP1 execution from cached witness data
• Block data for stats is fetched with a graceful fallback to zeroed entries if the RPC is unavailable

Test plan

• Run cargo run --bin multi --release -- --start 41900000 --end 41900100 --cache against a restricted RPC endpoint and verify no 403 errors
• Verify standard (non-cache) flow still works unchanged
• Verify --prove --cache path works from cached witness

[github-actions]

Metric	Value
Batch Start	14,268,645
Batch End	14,268,650
Witness Generation (seconds)	0
Execution Duration (seconds)	21
Total Instruction Count	521,761,865
Oracle Verify Cycles	61,755,147
Derivation Cycles	375,892,572
Block Execution Cycles	7,071,831
Blob Verification Cycles	23,426,259
Total SP1 Gas	804,143,739
Number of Blocks	5
Number of Transactions	5
Ethereum Gas Used	242,278
Cycles per Block	104,352,373
Cycles per Transaction	104,352,373
Transactions per Block	1
Gas Used per Block	48,455
Gas Used per Transaction	48,455
BN Pair Cycles	0
BN Add Cycles	0
BN Mul Cycles	0
KZG Eval Cycles	0
EC Recover Cycles	0
P256 Verify Cycles	0