[bug] test failure on 32-bit arches

heed was packaged for Debian; its testsuite fails on 32-bit arches:

470s running 20 tests
470s test env::tests::open_already_existing_database ... ok
470s test env::tests::open_database_with_writemap_flag ... ok
470s test env::tests::create_database_without_commit ... ok
470s test mdb::lmdb_error::test::test_description ... ok
470s test iterator::tests::rev_range_iter_last ... ok
470s test tests::error_is_send_sync ... ok
470s test env::tests::open_env_with_named_path ... ok
470s test iterator::tests::range_iter_last_with_byte_255 ... ok
470s test iterator::tests::iter_last ... ok
470s test env::tests::open_database_with_nosubdir ... ok
470s test env::tests::resize_database ... ok
470s test iterator::tests::rev_prefix_iter_last ... ok
470s test iterator::tests::prefix_iter_last_with_byte_255 ... ok
470s test iterator::tests::range_iter_last ... ok
470s test iterator::tests::rev_prefix_iter_last_with_byte_255 ... ok
470s test iterator::tests::prefix_iter_last ... ok
470s test env::tests::reopen_env_with_different_options_is_err ... ok
470s test iterator::tests::rev_range_iter_last_with_byte_255 ... ok
470s test env::tests::open_read_only_without_no_env_opened_before ... FAILED
471s test env::tests::close_env ... ok
471s 
471s failures:
471s 
471s ---- env::tests::open_read_only_without_no_env_opened_before stdout ----
471s thread 'env::tests::open_read_only_without_no_env_opened_before' panicked at src/env.rs:1030:27:
471s attempt to multiply with overflow
471s stack backtrace:
471s    0: rust_begin_unwind
471s              at /usr/src/rustc-1.80.1/library/std/src/panicking.rs:652:5
471s    1: core::panicking::panic_fmt
471s              at /usr/src/rustc-1.80.1/library/core/src/panicking.rs:72:14
471s    2: core::panicking::panic_const::panic_const_mul_overflow
471s              at /usr/src/rustc-1.80.1/library/core/src/panicking.rs:179:21
471s    3: heed::env::tests::open_read_only_without_no_env_opened_before
471s              at ./src/env.rs:1030:27
471s    4: heed::env::tests::open_read_only_without_no_env_opened_before::{{closure}}
471s              at ./src/env.rs:1023:53
471s    5: core::ops::function::FnOnce::call_once
471s              at /usr/src/rustc-1.80.1/library/core/src/ops/function.rs:250:5
471s    6: core::ops::function::FnOnce::call_once
471s              at /usr/src/rustc-1.80.1/library/core/src/ops/function.rs:250:5
471s note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
471s 
471s 
471s failures:
471s     env::tests::open_read_only_without_no_env_opened_before
471s 
471s test result: FAILED. 19 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 1.01s

Looks like this test exceeds the limit on those arches causing it to overflow.

Start with src/env.rs around lines 1023-1030 and run env::tests::open_read_only_without_no_env_opened_before on a 32-bit target. Trace the multiplication that overflows, then verify the test completes successfully on 32-bit architectures while the existing tests continue to pass.