restore: full snapshot resolve

[jvarela-jump]

Extends #9050 's http head resolve to the full snapshot.

Partially addresses #9091.

[Copilot]

Pull request overview

This PR extends the HTTP HEAD pre-resolve functionality to full snapshots, building upon PR #9050 which introduced the same mechanism for incremental snapshots. The goal is to validate the availability and freshness of snapshot data via HEAD requests before downloading, making the snapshot acquisition process more robust against stale gossip data.

Changes:

• Added full_resolve and full_resolve_peer fields to the fd_snapct_tile context structure for managing full snapshot HEAD pre-resolves
• Extended memory allocation in scratch_footprint and unprivileged_init to accommodate the new full snapshot resolver
• Updated rlimit_file_cnt to account for the additional socket needed by the full snapshot HEAD resolver
• Modified the FD_SNAPCT_STATE_COLLECTING_PEERS state in the snapshot acquisition state machine to perform HEAD pre-resolution for non-HTTPS peers before downloading full snapshots
• Added comprehensive validation logic for full snapshots (checking for proper snapshot type and staleness) and error handling for timeouts and failures
• Added HEAD resolver cancellation in reset states for both full and incremental snapshots
• Initialized the new full_resolve and full_resolve_peer fields in both privileged and unprivileged initialization functions

[github-actions]

Performance Measurements ⏳

Suite	Baseline	New	Change
backtest mainnet-406545575-perf per slot	0.137454 s	0.137142 s	-0.227% ✅
backtest mainnet-406545575-perf snapshot load	3.603 s	3.112 s	-13.628% ✅
backtest mainnet-406545575-perf total elapsed	137.453843 s	137.141694 s	-0.227% ✅
firedancer mem usage with mainnet.toml	1090.43 GiB	1090.43 GiB	0.000% ✅

[github-actions]

Performance Measurements ⏳

Suite	Baseline	New	Change
backtest mainnet-406545575-perf per slot	0.122205 s	0.122079 s	-0.103% ✅
backtest mainnet-406545575-perf snapshot load	3.362 s	2.772 s	-17.549% ✅
backtest mainnet-406545575-perf total elapsed	122.205089 s	122.079024 s	-0.103% ✅
firedancer mem usage with mainnet.toml	1090.43 GiB	1090.43 GiB	0.000% ✅

[github-actions]

Performance Measurements ⏳

Suite	Baseline	New	Change
backtest mainnet-406545575-perf per slot	0.143963 s	0.143993 s	0.021% ✅
backtest mainnet-406545575-perf snapshot load	5.287 s	3.593 s	-32.041% ✅
backtest mainnet-406545575-perf total elapsed	143.962727 s	143.992931 s	0.021% ✅
firedancer mem usage with mainnet.toml	1106.43 GiB	1090.43 GiB	-1.446% ✅