c/driver/postgresql: Get option for strings returns null terminator

[paleolimbot]

First noted here: #1129 (comment)

library(adbcdrivermanager)

adbc_database_init(
  adbcpostgresql::adbcpostgresql(),
  uri = Sys.getenv("ADBC_POSTGRESQL_TEST_URI")
) |> 
  adbc_connection_init() |>
  adbc_connection_get_option("adbc.connection.autocommit")
#> Error in adbc_connection_get_option(adbc_connection_init(adbc_database_init(adbcpostgresql::adbcpostgresql(),
#> :embedded nul in string: 'true\0'

It seems like this is intentional: https://github.com/apache/arrow-adbc/blob/main/c/driver/postgresql/connection.cc#L772-L776

...but I didn't expect it given the symmetry with getting bytes options and commitment to communicating the final size. Was it the intention that the null-terminator is included in the output size?

[lidavidm]

Intentional:

arrow-adbc/adbc.h

Lines 1587 to 1588 in 313245b

	/// to by value. If there is sufficient space, the driver will copy
	/// the option value (including the null terminator) to buffer and set

Because C strings expect null terminators so it's generally easier to just make sure it's there (like how std::string technically wouldn't need one because it tracks the length, but for interoperability it still tracks a null terminator anyways)