v1.58.5.0 fix: ignore missing flag values

[hiSandog]

Summary:

• Update shared flagValue parsing so a following --flag is not treated as the current flag's value.
• Add focused tests for present, missing, and next-flag cases.

Validation:

• /Users/sandog/.real/.bin/bun test test/bin-context.test.ts
• env PATH=/Users/sandog/.real/.bin:/opt/homebrew/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin /Users/sandog/.real/.bin/bun test test/gstack-decision-bins.test.ts
• git diff --check

[trunk-io]

Merging to main in this repository is managed by Trunk.

• To merge this pull request, check the box to the left or comment /trunk merge below.

After your PR is submitted to the merge queue, this comment will be automatically updated with its status. If the PR fails, failure details will also be posted here