Forward duplex option on fetchWithAgentSelection

[giovannibenussi]

Currently, we get the following error when making requests on the libsql/hrana-client-ts repository:

TypeError: RequestInit: duplex option is required when sending a body.

According to this issue, this option is required and, following the recommendation from this Chrome for Developers' article, we're setting its value to duplex: half as its default value if not provided because it was the only available value at least a year ago so makes sense to use as the default value too.

[khuezy]

Thanks, I was getting this too.