Add asfunction and typed_callable

[codecov[bot]]

Codecov Report

Patch coverage: 53.33% and project coverage change: -2.41 :warning:

Comparison is base (159cde8) 84.79% compared to head (c560e13) 82.38%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5 +/- ## ========================================== - Coverage 84.79% 82.38% -2.41% ========================================== Files 7 8 +1 Lines 171 176 +5 ========================================== Hits 145 145 - Misses 26 31 +5 ``` | [Impacted Files](https://app.codecov.io/gh/oschulz/FunctionChains.jl/pull/5?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Oliver+Schulz) | Coverage Δ | | |---|---|---| | [src/FunctionChains.jl](https://app.codecov.io/gh/oschulz/FunctionChains.jl/pull/5?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Oliver+Schulz#diff-c3JjL0Z1bmN0aW9uQ2hhaW5zLmps) | `100.00% <ø> (ø)` | | | [src/as\_function.jl](https://app.codecov.io/gh/oschulz/FunctionChains.jl/pull/5?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Oliver+Schulz#diff-c3JjL2FzX2Z1bmN0aW9uLmps) | `36.36% <36.36%> (ø)` | | | [src/function\_chain.jl](https://app.codecov.io/gh/oschulz/FunctionChains.jl/pull/5?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Oliver+Schulz#diff-c3JjL2Z1bmN0aW9uX2NoYWluLmps) | `90.00% <100.00%> (+1.32%)` | :arrow_up: |

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