Graceful client close (fix #36)

[Kylmakalle]

This one fixes #36 and makes the client close properly. However, trying to call client.run() immediately after the client.close() may result in non-working client. I assume this scenario is quite rare.

This PR does not interfere with public API much, except for some throws, but I believe nobody care about these two 404s "Client destroyed"

[XMLHexagram]

TDLibKit/scripts/tl2swift/Sources/TlParserLib/Composer/MethodsComposer.swift

Lines 192 to 239 in a4d1640

	if swiftAsync {
	return ""
	.addLine(Constants.asyncAvailableString)
	.addLine("private func execute<Q, R>(query: Q) async throws -> R where Q: Codable, R: Codable {")
	.addLine(" let dto = DTO(query, encoder: encoder)")
	.addLine(" return try await withCheckedThrowingContinuation { continuation in")
	.addLine(" do {")
	.addLine(" try client.send(query: dto) { result in")
	.addLine(" if let error = try? self.decoder.decode(DTO<Error>.self, from: result")) {
	.addLine(" continuation.resume(with: .failure(error.payload))")
	.addLine(" } else {")
	.addLine(" let response = self.decoder.tryDecode(DTO<R>.self, from: result)")
	.addLine(" continuation.resume(with: response.map { $0.payload })")
	.addLine(" }")
	.addLine(" }")
	.addLine(" } catch let err as Error {")
	.addLine(" continuation.resume(with: .failure(err))")
	.addLine(" } catch let any {")
	.addLine(" let err = Error(code: 500, message: any.localizedDescription)")
	.addLine(" continuation.resume(with: .failure(err))")
	.addLine(" }")
	.addLine(" }")
	.addLine("}")
	} else {
	return ""
	.addLine("private func execute<Q, R>(")
	.addLine(" query: Q,")
	.addLine(" completion: @escaping (Result<R, Swift.Error>) -> Void)")
	.addLine(" where Q: Codable, R: Codable {")
	.addBlankLine()
	.addLine(" let dto = DTO(query, encoder: encoder)")
	.addLine(" do {")
	.addLine(" try client.send(query: dto) { [weak self] result in")
	.addLine(" guard let strongSelf = self else { return }")
	.addLine(" if let error = try? strongSelf.decoder.decode(DTO<Error>.self, from: result) {")
	.addLine(" completion(.failure(error.payload))")
	.addLine(" } else {")
	.addLine(" let response = strongSelf.decoder.tryDecode(DTO<R>.self, from: result)")
	.addLine(" completion(response.map { $0.payload })")
	.addLine(" }")
	.addLine(" }")
	.addLine(" } catch let err as Error {")
	.addLine(" completion( .failure(err))")
	.addLine(" } catch let any {")
	.addLine(" let err = Error(code: 500, message: any.localizedDescription)")
	.addLine(" completion( .failure(err))")
	.addLine(" }")
	.addLine("}")

Please, also pay attention here, I think remove try! by using do catch and completion( .failure(err)) in the execute will make code much safer.

And I fix it in my PR #37.

[Kylmakalle]

@XMLHexagram addressed, thank you!