fix(internal/librarian/rust): update version bump to handle renamed dependencies

[jameslynnwu]

The version bump logic for Rust libraries is updated to correctly identify and update dependencies that have been renamed in the workspace manifest using the package field.

Previously, the logic only checked if the line started with the crate name, missing cases where the crate was aliased (like wkt for google-cloud-wkt). The new approach uses regular expressions to check for both direct names and the package field, while also ensuring we do not match commented-out lines.

Fixes #5365

[gemini-code-assist]

Code Review

This pull request updates the Rust manifest update logic to support renamed dependencies by using regular expressions to identify crate and package names. It also includes new test cases for these scenarios. A review comment pointed out that the packageRegex could fail if the keyword starts a line or if it appears within an inline comment, and provided a more robust regex suggestion to fix these issues.

[sofisl]

nit: with regex I add a test for "not-want"

[julieqiu]

Use string matching with strings.HasPrefix instead of regex, since it is more transparent and easier to understand that regex

[jameslynnwu]

Is this what you were looking for? Or did you also want to convert the isPackage check to prefix matching?

	lines := strings.Split(string(contents), "\n")
	updated := false
	packageRegex := regexp.MustCompile(fmt.Sprintf(`^\s*[^#]*\bpackage\s*=\s*"%s"`, regexp.QuoteMeta(crateName)))
	for i, line := range lines {
		trimmed := strings.TrimSpace(line)

		// Check if line starts with: crateName = ...
		isCrate := false
		if strings.HasPrefix(trimmed, crateName) {
			after := strings.TrimSpace(trimmed[len(crateName):])
			if strings.HasPrefix(after, "=") {
				isCrate = true
			}
		}

		// Check if line matches package regex
		isPackage := packageRegex.MatchString(line)
if (isCrate || isPackage) && versionRegex.MatchString(line) {