Incremental SMT2: Add size limit to array element retrieval

[tautschnig]

Add MAX_TRACE_ARRAY_SIZE (1000) threshold to get_expr for array_typet. When an array exceeds this size, return empty optional with a warning instead of enumerating all elements, which caused OOM for large arrays (e.g., __CPROVER_max_malloc_size = 2^23).

The caller in get() already handles empty optional gracefully by falling back to returning the original expression.

Also remove the no-new-smt exclusion tag from pointer-offset-01 test since this fix prevents the OOM that required the exclusion.

Fixes: #8071

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