feat: xev Dynamic API + gitignore updates for Shadow support

[GrapeBaBa]

Summary

• Switch xev from compile-time backend selection to Dynamic API for runtime io_uring/epoll detection
• This makes the binary portable across Linux kernel versions and Shadow-compatible
• Add gitignore entries for zig-pkg/ cache, Shadow simulator outputs, and IDE files

Details

xev Dynamic API

All @import("xev") changed to @import("xev").Dynamic, which probes io_uring at runtime and falls back to epoll. A detectBackend() helper in utils.zig is called early in main and in test setup.

gitignore

• zig-pkg/ — local Zig package cache (should not be committed)
• shadow.yaml, shadow.data/ — generated by lean-quickstart/run-shadow.sh
• .idea/ — JetBrains IDE files

Test plan

• Verify build passes on CI
• Verify existing tests pass
• Verify Shadow 4-node devnet works with lean-quickstart/run-shadow.sh

[Copilot]

Pull request overview

This PR updates the Zig codebase to use libxev’s Dynamic API so the runtime can select the best available I/O backend (io_uring vs epoll), improving portability across Linux kernel versions and compatibility with Shadow. It also updates .gitignore to exclude additional local/tool-generated artifacts.

Changes:

• Switched @import("xev") usages to @import("xev").Dynamic across node, network, and CLI code.
• Added a detectBackend() helper and invoked it early in CLI startup and node test initialization.
• Updated .gitignore to ignore zig-pkg/, Shadow outputs, and .idea/.

Reviewed changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
pkgs/node/src/utils.zig	Introduces detectBackend() and moves node code to xev.Dynamic.
pkgs/node/src/testing.zig	Calls backend detection before initializing the event loop in tests.
pkgs/node/src/node.zig	Switches xev import for tests to xev.Dynamic.
pkgs/node/src/lib.zig	Re-exports detectBackend for external callers (CLI).
pkgs/node/src/clock.zig	Switches xev import to xev.Dynamic.
pkgs/network/src/mock.zig	Switches to xev.Dynamic and adds backend detection in tests.
pkgs/network/src/interface.zig	Switches xev import to xev.Dynamic.
pkgs/network/src/ethlibp2p.zig	Switches xev import to xev.Dynamic.
pkgs/cli/src/node.zig	Switches xev import to xev.Dynamic.
pkgs/cli/src/main.zig	Calls node_lib.detectBackend() early during CLI startup.
build.zig	Notes that xev backend override is no longer needed.
.gitignore	Ignores zig-pkg/, Shadow outputs, and JetBrains IDE files.

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[Copilot]

xev.detect() failures are turned into a generic @panic("no available xev backend"), which drops the underlying error and makes field debugging hard (e.g., missing io_uring support vs. permission issues). Consider including the caught error (e.g., @errorName(err) / {any}) in the panic message or returning an error instead of panicking so callers can surface it consistently.

Suggested change

	xev.detect() catch @panic("no available xev backend");
	xev.detect() catch |err| std.debug.panic("no available xev backend: {s}", .{@errorName(err)});

[Copilot]

This if (@hasDecl(xev, "detect")) xev.detect() ... backend-detection snippet is duplicated in multiple tests in this file. Consider factoring it into a small local helper (e.g., detectBackendOrPanic()), so the behavior/error handling stays consistent and future changes only need to be made once.

[Copilot]

This backend detection line duplicates the same xev.detect() snippet used earlier in this file. To reduce repetition (and keep the panic/error message consistent), consider extracting the detection into a single helper and calling it from each test before xev.Loop.init.

[Copilot]

node_lib.detectBackend() currently panics on failure (see utils.detectBackend), which bypasses the CLI’s normal ErrorHandler flow and will crash the process with a generic message. Consider changing detection to return an error and handling/logging it here (similar to the xev.Loop.init error handling below) so startup failures are reported consistently.

Suggested change

	node_lib.detectBackend();
	node_lib.detectBackend() catch |err| {
	ErrorHandler.logErrorWithOperation(err, "detect I/O backend");
	return err;
	};