fix(sync): return error instead of panicking on get_account proof with no details

[erhnysr]

Summary

StateSync::validate_account_proof unwrapped the optional account details from a get_account proof with .expect("node returned no details for a public account"), treating their presence as an invariant. But AccountProof allows details: None end-to-end — the RPC conversion layer in rpc/domain/account.rs produces None when the response omits them — so a malformed, buggy, or malicious node response crashes the client with a panic mid-sync instead of surfacing a validation error.

This is the same class of untrusted-input hardening as the recent VerifyingRpcClient fixes (#2419, #2381): a value the node controls was trusted without being checked.

The bug

crates/rust-client/src/sync/state_sync.rs

Ok(details.expect("node returned no details for a public account"))

Reachable during public account sync: the proof reaches validate_account_proof, passes the block / account-id / witness checks, then panics on the final .expect() if details is None.

The fix

Return ClientError::ChainValidationError when details are absent, consistent with the function's other validation failures:

details.ok_or_else(|| {
    ClientError::ChainValidationError(format!(
        "get_account returned no details for public account {account_id}"
    ))
})

The # Panics doc section is replaced with a fourth # Errors bullet, and a regression test (validate_account_proof_rejects_missing_details) builds an otherwise-honest proof with the details stripped and asserts ChainValidationError.

Verification

• make lint — clean (cargo fix, cargo +nightly fmt, taplo fmt, cargo clippy --workspace --features "testing std" --all-targets -- -D warnings, cargo shear all pass, no warnings)
• make test — 458 tests run: 458 passed, 2 skipped; the new regression test passes

Closes #2386

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[igamigo]

Leaving some comments. Also, can you resolve conflicts?

[erhnysr]

Hi @igamigo — Integration tests failed on network_fpi (bin/integration-tests/src/tests/network_fpi.rs:143, the counter assertion), but this looks like a pre-existing flake unrelated to this PR: the network transaction did not increment the counter within wait_for_blocks(2) (left: Word([0,0,0,0]) vs right: Word([1,0,0,0])). The same test failed identically on next in run #34228789999 (the push for #2479, which does not touch state_sync.rs). Unit tests and doc tests are green.

Could you re-run the Integration tests job when you get a chance? (Fork PR workflows need maintainer approval to re-run.)

Also addressed both your review comments in the latest commits (888100d) — replying on those threads separately.