chore: upgrade rust toolchain to 1.78.0

[hanabi1224]

• upgrade rust toolchain to 1.78.0
• fix new clippy warnings

warning: bound is defined in more than one place
   --> ipld/hamt/src/node.rs:229:18
    |
229 |     fn get_value<Q: ?Sized, S: Blockstore>(
    |                  ^
...
239 |         Q: Eq + Hash,
    |         ^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#multiple_bound_locations

warning: unnecessary use of `get(&h2).is_none()`
   --> shared/tests/address_test.rs:584:16
    |
584 |     assert!(hm.get(&h2).is_none());
    |             ---^^^^^^^^^^^^^^^^^^
    |             |
    |             help: replace it with: `!hm.contains_key(&h2)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_get_then_check

[hanabi1224]

@rvagg Good point, updated clippy warning details in the PR description.

[rvagg]

ah, those are nice lints, thanks