Add a flake check for testing the stdlib

[jneem]

An amusing little thing that I think is harmless: when a test in the stdlib uses the std name (like std.contract.not) then it's testing the copy of the stdlib that was compiled into the nickel binary. But when it uses a "local" name (like HasField) then it's testing the copy of the stdlib that it gets from the path ./core/stdlib/std.ncl.

[github-actions[bot]]

Bencher Report

Branch	2061/merge
Testbed	ubuntu-latest

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Benchmark	Latency	nanoseconds (ns)
fibonacci 10	📈 view plot ⚠️ NO THRESHOLD	497,790.00
pidigits 100	📈 view plot ⚠️ NO THRESHOLD	3,241,700.00
product 30	📈 view plot ⚠️ NO THRESHOLD	842,070.00
scalar 10	📈 view plot ⚠️ NO THRESHOLD	1,531,500.00
sum 30	📈 view plot ⚠️ NO THRESHOLD	839,480.00

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[yannham]

An amusing little thing that I think is harmless: when a test in the stdlib uses the std name (like std.contract.not) then it's testing the copy of the stdlib that was compiled into the nickel binary. But when it uses a "local" name (like HasField) then it's testing the copy of the stdlib that it gets from the path ./core/stdlib/std.ncl.

Yeah, it's the same for the actual stdlib code - often functions refer to other function of the same module directly, but use std to access outer module (in some places this was required because of the typechecking not being the same - I don't know if it's the case anymore with the polymorphism rework but it might be).