fix(filter): don't treat /* inside strings as a block comment

[luccinmasirika]

Summary

Fixes #2385. The minimal code filter dropped real code lines that happened to contain /*.

MinimalFilter opened a block comment whenever a line contained /* (trimmed.contains(start)), so:

• a /* inside a string literal or a trailing comment dropped the whole line;
• if that line had no matching */, every following line was dropped too until one showed up.

let re = "start /*";   // dropped
let x = 5;             // dropped (still "inside" the phantom comment)

Fix

Match the opening marker with starts_with instead of contains — the same way line comments are already detected one block below. Only a line that actually begins with /* opens a block comment; doc blocks (/**) are still preserved, and genuine standalone/multi-line block comments are still stripped.

Tests

• test_minimal_filter_keeps_code_with_block_comment_markers — code with /* in a string / trailing comment is preserved (fails on the old contains version, passes now).
• test_minimal_filter_still_strips_block_comments — standalone and multi-line block comments are still removed.

Verified end-to-end with the issue's reproduction:

$ rtk read example.rs --level minimal
const API: &str = "http://example.com/v1"; // endpoint
let re = "start /*";
let pattern = "/* not a comment */";
let x = 5; /* inline note */
fn foo() {}

(only the standalone /* ... */ line is stripped; no code is lost).

Pre-commit gate (cargo fmt --all && cargo clippy --all-targets && cargo test) passes; clippy is clean.

[CLAassistant]

All committers have signed the CLA.

[luccinmasirika]

Closing as a duplicate — #2397 already fixes this with the same line-start detection and predates this PR. Deferring to it. Thanks @hgunduzoglu!