Review forge lint "unsafe-typecast"

My brief examination found these were all false positives, but as a follow-up to https://github.com/FilOzone/pdp/pull/290, we want to look over them to see if any are worth fixing. In some cases these truncations are intentional. In other cases they are harmless.

Do not add guards against impossible situations.

Assume that parameters supplied by the owner will be reasonable, though certain footguns may still be worth protecting against, depending on the impact.

Do not change function signatures.

Prefer to leave this lint disabled if there are more than 2 false-positives remaining in the codebase rather than proliferating `forge-lint: disable-next-line(unsafe-typecast)`.

Start with the unsafe-typecast findings from follow-up pull request #290 and inspect each reported truncation in the codebase. Decide whether it is intentional, harmless, or worth fixing without adding impossible-case guards or changing signatures; the review is done when the findings are addressed and the lint remains disabled if more than two false positives remain.

Written by the indexing model from the issue text.