Added a new function, `WriteProtoFiles` in `desc_source.go` which is used to generate .proto files. The process involves resolving symbols from the descriptor source and writing their definitions to a designated output directory. The corresponding flag `--proto-out` has been included in `grpcurl.go` to allow users to specify the directory path.
* update to latest jhump/protoreflect
* be lenient when possible if server cannot furnish all dependencies
* move linting back to go 1.21 instead of latest go 1.22
* make staticcheck happy
* organize into multiple files
* make listing methods show fully-qualified names
* address small feedback from recent change (trim then check if empty)
Eitol