fix(backoff): fibonacci delay should cap on max delay

[dentiny]

Closes #231

[dentiny]

error: creating a new box
   --> backon-macros/src/lib.rs:100:9
    |
100 |         item_fn.block = Box::new(block);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: replace existing content with inner value instead: `*item_fn.block = block`
    |
    = note: this creates a needless allocation
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.94.0/index.html#replace_box
    = note: `-D clippy::replace-box` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::repla

The failed CI doesn't seem to be related to my change

[dentiny]

Nightly unit failure also seems unrelated

EXPECTED:
┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈
error: `adjust` is only available for async functions
 --> tests/cases/fail_adjust_blocking.rs:8:4
  |
8 | fn invalid_blocking() -> Result<(), &'static str> {
  |    ^^^^^^^^^^^^^^^^

error[E0425]: cannot find function `invalid_blocking` in this scope
  --> tests/cases/fail_adjust_blocking.rs:13:13
   |
13 |     let _ = invalid_blocking();
   |             ^^^^^^^^^^^^^^^^ not found in this scope
┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈

ACTUAL OUTPUT:
┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈
error: `adjust` is only available for async functions
 --> tests/cases/fail_adjust_blocking.rs:8:4
  |
8 | fn invalid_blocking() -> Result<(), &'static str> {
  |    ^^^^^^^^^^^^^^^^
┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈
note: If the actual output is the correct output you can bless it by rerunning
      your test with the environment variable TRYBUILD=overwrite

test tests/cases/fail_context_ident.rs [should fail to compile] ... ok
test tests/cases/fail_method_self_context.rs [should fail to compile] ... ok
test tests/cases/fail_method_mut_context.rs [should fail to compile] ... ok
test tests/cases/fail_context_value_self.rs [should fail to compile] ... ok


test trybuild_suite ... FAILED

failures:

---- trybuild_suite stdout ----