feat: extract noteguard-core library crate

[alltheseas]

Summary

Extracts the core filtering logic into a standalone library crate (noteguard-core) that can be embedded in any Nostr relay, not just strfry.

• New noteguard-core crate with filter registry, pipeline executor, and all built-in filters
• noteguard binary refactored to be a thin stdin/stdout wrapper using noteguard-core
• Updated README with library usage documentation

Motivation

This addresses #9 by making noteguard's filtering logic available as a library. Other relays (like notepush) can now embed noteguard filtering directly to prevent DoS attacks from spam that triggers expensive remote operations.

Using noteguard-core

[dependencies]
noteguard-core = { git = "https://github.com/damus-io/noteguard" }

use noteguard_core::{Noteguard, Config, Action};

let config: Config = toml::from_str(config_str)?;
let mut guard = Noteguard::new();
guard.load_config(&config)?;

let output = guard.run(input_message);
match output.action {
    Action::Accept => { /* process event */ },
    Action::Reject | Action::ShadowReject => { /* drop event */ },
}

Test plan

• All existing tests pass (cargo test)
• Binary builds and runs correctly
• Library can be imported and used by downstream crates

🤖 Generated with Claude Code

[jb55]

noteguard should be the library name, note noteguard_core

[alltheseas]

cca48d1

fixed in cca48d1

also updated notepush damus-io/notepush@3e742da accordingly

[alltheseas]

@coderabbitai review please

[coderabbitai]

@alltheseas, I'll review the changes in this PR.

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📥 Commits

Reviewing files that changed from the base of the PR and between 4d4d9d6 and cca48d1.

⛔ Files ignored due to path filters (1)

• Cargo.lock is excluded by !**/*.lock

📒 Files selected for processing (14)

• Cargo.toml
• README.md
• src/filters/blacklist.rs
• src/filters/content.rs
• src/filters/forwarder.rs
• src/filters/kinds.rs
• src/filters/mod.rs
• src/filters/protected_events.rs
• src/filters/ratelimit.rs
• src/filters/whitelist.rs
• src/lib.rs
• src/main.rs
• src/messages.rs
• src/note_filter.rs

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