RequestedRange::as_proto casts u64 to i64 without clamping

Unconfirmed. This is the result of a search with Claude, may be a false positive.

In `src/storage/src/storage/bidi/requested_range.rs`, `RequestedRange::as_proto` converts range offsets and lengths to protobuf fields using raw `as i64` casts:

https://github.com/googleapis/google-cloud-rust/blob/f02b42c2ac5720334cd2b5335824bd4166264527/src/storage/src/storage/bidi/requested_range.rs#L26-L40

For `ReadRange::offset(u64::MAX)`, `u64::MAX as i64` produces `read_offset: -1`. Additionally, computing `-(v as i64)` for `ReadRange::tail(1 << 63)` overflows and panics in debug builds.

Start in src/storage/src/storage/bidi/requested_range.rs at RequestedRange::as_proto and inspect how offsets and lengths become protobuf fields. Reproduce the ReadRange::offset(u64::MAX) and ReadRange::tail(1 << 63) cases, then add coverage showing conversions are safely bounded and do not panic.

Written by the indexing model from the issue text.