feat(pxe): speculatively sync predicted contract call trees

[AztecBot]

Port of #25214 onto merge-train/fairies.

Note on the two-commit request: The cherry-pick applied cleanly with no conflicts, so there's nothing to split into a separate resolution commit. Single squashed commit only — happy to redo it as a two-commit stack if you'd rather see an explicit empty-resolution commit, but that would just be a no-op.

Original description:

PXE syncs contracts serially as execution reaches them: each nested call discovers the next contract only after the previous sync completes, so multi-contract transactions pay one sync round trip per hop.

PXE learns a per-function call graph from the calls each committed job observed (ContractCallGraph). When a sync request arrives, the sync service speculatively starts the syncs of every contract the invoked function is predicted to call, recursing through each callee's own predictions, and also speculates from each contract's sync_state, which runs during the sync itself (#25164). A per-job set of already-speculated functions stops the recursion when the predicted graph has a cycle. Mispredicting is cheap: the extra node requests batch into round trips the job already makes, and the synced data goes unused.

Beyond the straight port, settle changes semantics vs #25126: it tracks only the speculative syncs and rejects with an AggregateError when any failed, so the job discards its staged writes instead of committing them. A speculative failure might not be surfaced by any request, and a sync that fails midway can leave partial staged writes. Stacked on #25208, whose allToCompletion runs the parallel staged-write branches to completion on failure.

The feature is gated behind PXE_CONCURRENT_CONTRACT_SYNC_ENABLED (default off, experimental).

Cherry-pick of merge commit cee7f40ca9c7d53b0d6af2d0175139606cc48f7c (git cherry-pick -m 1), applied cleanly on top of merge-train/fairies.

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Created by claudebox · group: slackbot · requested by Nico Chamo · Slack thread