[feature request] String interpolation for logging

In Python, there's a useful little feature that allows writing something like the following:

foo = "bar"
print(f"{foo = }")

which prints:

foo = 'bar'

Notice how it preserved the spaces before and after the equals sign as written in the f-string.

I think this feature would be a very nice addition to Yuescript, although it may need some simplification. In Python, the code actually translates to printing the repr of foo, not the string conversion; an equivalent would be to write print("foo = " + repr(foo)). But of course that doesn't exist in Lua. My suggestion would be to either just print the value's tostring(), or maybe using a library function to pretty print it. While Yuescript seems to generally prefer inlining things to prevent being dependent on any libraries, I believe it would be fine here, because this is a pure development/debugging feature, so it's pretty safe to expect someone to have Yuescript installed if their code makes use of it.

The issue describes Python's self-documenting f-string syntax and proposes a Yuescript equivalent with either tostring-style output or pretty printing. Start by resolving the intended syntax and value representation from these alternatives; done means the feature's behavior and spacing around the equals sign are agreed and implemented.