## Description 

`simulate_transaction` duplicated validation logic from the signing path
but had diverged: it called `process_funds_withdrawals_for_execution`
(which uses `.unwrap()`) instead of the safe
`process_funds_withdrawals_for_signing` (which returns `Result`),
meaning a malformed transaction could panic a fullnode during
simulation. This extracts the shared pre-object-load validation — deny
checks, funds withdrawal parsing, and balance availability checks — into
`pre_object_load_checks`, called by both
`handle_transaction_deny_checks` and `simulate_transaction`, fixing the
panic and ensuring the two paths stay in sync.

## Test plan 

- `cargo check -p sui-core` — compiles cleanly
- `SUI_SKIP_SIMTESTS=1 cargo nextest run -p sui-core` — all tests pass
- `cargo xclippy` — no warnings

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## Release notes

Check each box that your changes affect. If none of the boxes relate to
your changes, release notes aren't required.

For each box you select, include information after the relevant heading
that describes the impact of your changes that a user might notice and
any actions they must take to implement updates.

- [ ] Protocol: 
- [x] Nodes (Validators and Full nodes): Fixes a potential fullnode
panic when simulating a malformed transaction with invalid funds
withdrawals.
- [ ] gRPC:
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:
- [ ] Indexing Framework: