Fix typos in documentation

[Marcofann]

This pull request addresses several minor typographical errors in both documentation and source code files to improve clarity and readability.

Files Updated:

1. background.md: Corrected "an specific" to "a specific."
2. anonymous-components-and-tuples.md: Replaced "an statement" with "a statement."
3. memory_slice.rs: Fixed "a element" to "an element."
4. constants_handler.rs: Changed "a expression" to "an expression."

[Marcofann]

@miguelis Hi!

I decided to proactively combine all changes into a single commit, as I noticed you requested this from other contributors