Safety condition review

[ethe]

fusio uses a set of unsafe block (especially in buffer read / write behaviors) to ensure that the performance is the same as natives, please check them at https://github.com/search?q=repo%3Atonbo-io%2Ffusio%20unsafe&type=code, I tried my best to keep them simple and small, however, it has not been widely reviewed by community, we should:

• check all unsafe block, identify whether it should be an unsafe block
• evaluate specific safety condition to each block
• prevent undefined behavior