lint: allow self-documenting builder arguments

[anp-oai]

Builder-style setters often repeat the setting name in both the method and its sole argument. Calls such as .enabled(false) are already self-documenting, so requiring /*enabled*/ adds noise without clarifying the call.

What changed

• Exempt a method's sole non-self argument when its resolved parameter name matches the method name.
• Continue validating any explicit argument comment against the resolved parameter name.
• Continue requiring comments when method and parameter names differ or when a method has multiple non-self arguments.
• Document the exception in AGENTS.md and the lint's own behavior documentation.

Examples

Before this change we'd need redundant comments like this:

builder.enabled(/*false*/ false);
builder.retry_count(/*retry_count*/ 3);
builder.base_url(/*base_url*/ None);

Now can be written like this:

builder.enabled(false);
builder.retry_count(3);
builder.base_url(None);

Still disallowed:

client.set_flag(true); // Method name does not match parameter `enabled`.
options.enabled(false, /*retry_count*/ 3); // More than one non-self argument.
options.enabled(/*value*/ false); // Explicit comment does not match `enabled`.

Validation

Added UI coverage for boolean, numeric, and None builder arguments, multi-argument methods, and explicit comment mismatches. Ran rustup run nightly-2025-09-18 cargo test in tools/argument-comment-lint.