Flush `stdout` unconditionally

Description of the change

This commit ensures that stdout is always correctly flushed after writing to it. This is critical for dynamic use-cases of Javy

[x] I've updated the relevant CHANGELOG files if necessary. Changes to javy-cli and javy-core do not require updating CHANGELOG files.
[x] I've updated the relevant crate versions if necessary. Versioning policy for library crates
[x] I've updated documentation including crate documentation if necessary.