add one-liner parser APIs and clean warnings

[tiye]

Summary

• add MoonBit one-liner parser and formatter APIs to match the Rust implementation
• add regression coverage for one-liner parsing/formatting
• clean MoonBit warnings so moon test is clean

Testing

• moon test

[Copilot]

Pull request overview

This PR adds MoonBit “one-liner” parser/formatter APIs for Cirru expressions (to align with the Rust implementation), expands regression tests for one-liner round-tripping, and performs small warning-cleanup refactors.

Changes:

• Add Cirru::parse_expr_one_liner and one-liner formatting APIs (format_expr_one_liner + format_one_liner).
• Implement one-liner statement formatting logic in the writer.
• Add regression tests for one-liner parse/format round-trip and error cases; apply small refactors to remove warnings.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/writer.mbt	Adds one-liner expression formatter and related helper logic; minor boolean/style tweaks.
src/parser.mbt	Adds parse_expr_one_liner API to require exactly one expression result.
src/primes.mbt	Adds Cirru::format_one_liner convenience method.
src/parser_test.mbt	Adds regression coverage for one-liner parsing/formatting and rejection of multiple expressions.
src/tree.mbt	Refactors looping / slice conversion to address warnings.
src/s_expr.mbt	Refactors boolean/slice conversion to address warnings.
README.md	Documents new one-liner APIs.

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[Copilot]

generate_statement_one_liner returns an empty string when xs is empty, so Cirru::format_expr_one_liner(List([])) would format to "" instead of the valid empty expr representation "()". Add an explicit empty-case (e.g., return generate_empty_expr() / "()") and consider adding a regression test for formatting/parsing an empty expression.

Suggested change

	fn generate_statement_one_liner(xs : Array[Cirru]) -> String {
	fn generate_statement_one_liner(xs : Array[Cirru]) -> String {
	if xs.is_empty() {
	return generate_empty_expr()
	}

[Copilot]

Tail $ formatting here is triggered for any last List element (idx > 0 && idx == size - 1). In the main formatter (generate_tree), tail handling only applies when the previous node is a Leaf (prev_kind == Leaf). To keep one-liner formatting consistent/canonical, compute at_tail using the previous element kind (e.g., only treat the last list as tail when it is immediately preceded by a leaf).