chore: use mod.nr files in stdlib (#5379)

# Description

## Problem\*

Followup to #5039 

## Summary\*

This PR pushes all `hash.nr` into the `hash` directory as a `mod.nr`
file, etc.

## Additional Context



## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

docs/docs/noir/standard_library/cryptographic_primitives/ec_primitives.md

@@ -18,7 +18,7 @@ curve you want to use, which would be specified using any one of the methods
 `std::ec::{tecurve,montcurve,swcurve}::{affine,curvegroup}::new` which take the coefficients in the
 defining equation together with a generator point as parameters. You can find more detail in the
 comments in
-[`noir_stdlib/src/ec.nr`](https://github.com/noir-lang/noir/blob/master/noir_stdlib/src/ec.nr), but
+[`noir_stdlib/src/ec/mod.nr`](https://github.com/noir-lang/noir/blob/master/noir_stdlib/src/ec/mod.nr), but
 the gist of it is that the elliptic curves of interest are usually expressed in one of the standard
 forms implemented here (Twisted Edwards, Montgomery and Short Weierstraß), and in addition to that,
 you could choose to use `affine` coordinates (Cartesian coordinates - the usual (x,y) - possibly
@@ -67,7 +67,7 @@ does indeed lie on `c` by calling `c.contains(p1)`.
   the curve configurations, the SWU map-to-curve method may be called as `c.swu_map(z,n)`, where
   `z: Field` depends on `Field` and `c` and must be chosen by the user (the conditions it needs to
   satisfy are specified in the comments
-  [here](https://github.com/noir-lang/noir/blob/master/noir_stdlib/src/ec.nr)).
+  [here](https://github.com/noir-lang/noir/blob/master/noir_stdlib/src/ec/mod.nr)).
 
 ## Examples
 

docs/docs/noir/standard_library/cryptographic_primitives/hashes.mdx

@@ -15,7 +15,7 @@ import BlackBoxInfo from '@site/src/components/Notes/_blackbox.mdx';
 Given an array of bytes, returns the resulting sha256 hash.
 Specify a message_size to hash only the first `message_size` bytes of the input.
 
-#include_code sha256 noir_stdlib/src/hash.nr rust
+#include_code sha256 noir_stdlib/src/hash/mod.nr rust
 
 example:
 #include_code sha256_var test_programs/execution_success/sha256/src/main.nr rust
@@ -34,7 +34,7 @@ fn main() {
 
 Given an array of bytes, returns an array with the Blake2 hash
 
-#include_code blake2s noir_stdlib/src/hash.nr rust
+#include_code blake2s noir_stdlib/src/hash/mod.nr rust
 
 example:
 
@@ -51,7 +51,7 @@ fn main() {
 
 Given an array of bytes, returns an array with the Blake3 hash
 
-#include_code blake3 noir_stdlib/src/hash.nr rust
+#include_code blake3 noir_stdlib/src/hash/mod.nr rust
 
 example:
 
@@ -68,7 +68,7 @@ fn main() {
 
 Given an array of Fields, returns the Pedersen hash.
 
-#include_code pedersen_hash noir_stdlib/src/hash.nr rust
+#include_code pedersen_hash noir_stdlib/src/hash/mod.nr rust
 
 example:
 
@@ -80,7 +80,7 @@ example:
 
 Given an array of Fields, returns the Pedersen commitment.
 
-#include_code pedersen_commitment noir_stdlib/src/hash.nr rust
+#include_code pedersen_commitment noir_stdlib/src/hash/mod.nr rust
 
 example:
 
@@ -94,7 +94,7 @@ Given an array of bytes (`u8`), returns the resulting keccak hash as an array of
 32 bytes (`[u8; 32]`). Specify a message_size to hash only the first
 `message_size` bytes of the input.
 
-#include_code keccak256 noir_stdlib/src/hash.nr rust
+#include_code keccak256 noir_stdlib/src/hash/mod.nr rust
 
 example: