feat: add CLOSE_GROUP_SIZE and CLOSE_GROUP_MAJORITY constants

[mickvandijke]

Summary

• Adds CLOSE_GROUP_SIZE (5) and CLOSE_GROUP_MAJORITY (3) constants to ant_protocol
• Re-exports both from the crate root so downstream consumers can use ant_node::CLOSE_GROUP_SIZE
• Replaces the local REQUIRED_QUOTES constant in the payment module with the canonical CLOSE_GROUP_SIZE

Test plan

• cargo build passes
• cargo test --no-run compiles all tests
• cargo fmt and cargo clippy clean

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR centralizes the network “close group” sizing into ant_protocol by introducing CLOSE_GROUP_SIZE (5) and CLOSE_GROUP_MAJORITY (3), then updates payment logic to use the canonical constant and re-exports the constants from the crate root for downstream use.

Changes:

• Added CLOSE_GROUP_SIZE and CLOSE_GROUP_MAJORITY constants to src/ant_protocol/mod.rs.
• Re-exported these constants from src/lib.rs so consumers can use ant_node::CLOSE_GROUP_SIZE.
• Replaced the payment module’s local quote-count constant usage with CLOSE_GROUP_SIZE.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

File	Description
src/payment/verifier.rs	Uses CLOSE_GROUP_SIZE for quote-count validation and updates related test comment.
src/payment/single_node.rs	Removes the local required-quote constant and switches fixed-size arrays/validations to CLOSE_GROUP_SIZE.
src/lib.rs	Re-exports CLOSE_GROUP_SIZE / CLOSE_GROUP_MAJORITY from the crate root.
src/ant_protocol/mod.rs	Defines and documents the close-group sizing constants.

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[Copilot]

This test constructs 5 quotes using a hard-coded loop bound (0..5) while the enforcement now uses CLOSE_GROUP_SIZE. Use CLOSE_GROUP_SIZE (and consider updating the other similar loops in this test module) so the test stays consistent if the constant changes.

Suggested change

	// Build 5 quotes with distinct peer IDs (required by CLOSE_GROUP_SIZE enforcement)
	let mut peer_quotes = Vec::new();
	for _ in 0..5 {
	// Build CLOSE_GROUP_SIZE quotes with distinct peer IDs (required by CLOSE_GROUP_SIZE enforcement)
	let mut peer_quotes = Vec::new();
	for _ in 0..CLOSE_GROUP_SIZE {