Improved support for Julia 1.11+

[krrutkow]

• drops Julia 1.5 support, adds 1.12+
• stops generating duplicate definitions for types declared in function return/arguments
• fixes tests to not cause duplicate definitions to occur
• no longer uses the deprecated clang() do method of calling the binary
• returns 0 and () when getting field count/names opaque types instead of throwing an error
• bumps package version to 1.1.0