Provide API to tune the balancing factors used in conversion

[kanru]

Is your feature request related to a problem? Please describe.

酷音的「注音→詞」轉換引擎有一組規則用來計算最佳的斷詞方式

https://github.com/chewing/libchewing/blob/073e7c0ceb9c4a83d7c2241c7a9548ca5fceebcb/src/conversion/chewing.rs#L470-L475

這些權重應該要是可以調整的。

Describe the solution you'd like

提供 API 讓進階使用者可以預覽並調整權重

Describe alternatives you've considered

Use environment variable or config files.