Rework Buffer block

[imunproductive]

This PR reworks current Buffer block. It adds another input to act as a trigger to output already stored messages received in main input port.

Here is the simplest example that would buffer a string and then output it each time ReadStdin block outputs anything (on new line).

use protoflow_blocks::*;
fn main() {
	System::run(|s| {
		let stdin = s.read_stdin();
		let hello = s.const_string("Hello, World!");
		let encode = s.encode_lines();
		let buffer = s.buffer();
		let stdout = s.write_stdout();
		s.connect(&hello.output, &encode.input);
		s.connect(&encode.output, &buffer.input);
		s.connect(&stdin.output, &buffer.trigger);
		s.connect(&buffer.output, &stdout.input);
	});
}

I am not sure what to do with StdioSystem implementation so for now I left it as it was before, meaning it just eats input and outputs nothing.

[artob]

@race-of-sloths invite

[race-of-sloths]

@imunproductive Thank you for your contribution! Your pull request is now a part of the Race of Sloths!
We are launching a survey "Who is faster? You vs SpaceX"

Current status: stale

This pull request was removed from the race, but you can include it again with @race-of-sloths include command

What is the Race of Sloths

Race of Sloths is a friendly competition where you can participate in challenges and compete with other open-source contributors within your normal workflow

For contributors:

• Tag @race-of-sloths inside your pull requests
• Wait for the maintainer to review and score your pull request
• Check out your position in the Leaderboard
• Keep weekly and monthly streaks to reach higher positions
• Boast your contributions with a dynamic picture of your Profile

For maintainers:

• Score pull requests that participate in the Race of Sloths and receive a reward
• Engage contributors with fair scoring and fast responses so they keep their streaks
• Promote the Race to the point where the Race starts promoting you
• Grow the community of your contributors

Feel free to check our website for additional details!

Bot commands

• For contributors
  • Include a PR: @race-of-sloths include to enter the Race with your PR
• For maintainers:
  • Invite contributor @race-of-sloths invite to invite the contributor to participate in a race or include it, if it's already a runner.
  • Assign points: @race-of-sloths score [1/2/3/5/8/13] to award points based on your assessment.
  • Reject this PR: @race-of-sloths exclude to send this PR back to the drawing board.
  • Exclude repo: @race-of-sloths pause to stop bot activity in this repo until @race-of-sloths unpause command is called

[github-actions]

⚠️ CI failed

Platform	Name	Status	Details
All	Formatting	✅	Details
Linux	Build library	❌	Details
Linux	Build binaries	❌	Details
Linux	Build tests	❌	Details
Linux	Build examples	❌	Details
Linux	Run tests	⏩	Details
Linux	Run doctests	⏩	Details

[artob]

@race-of-sloths score 8

[github-actions]

⚠️ CI failed

Platform	Name	Status	Details
All	Formatting	✅	Details
Linux	Build library	❌	Details
Linux	Build binaries	❌	Details
Linux	Build tests	❌	Details
Linux	Build examples	❌	Details
Linux	Run tests	⏩	Details
Linux	Run doctests	⏩	Details

[artob]

Important

Protoflow has been discontinued and archived in favor of its successors Async-Flow and Flows.rs, which represent the future of flow-based programming in Rust and offer a substantially better developer experience as well as simply higher development velocity. We aim to eventually port the functionality in this pull request over to Flows.rs; if you'd like to contribute to make that happen sooner, please raise an issue and/or pull request against that repository.