feat: macros package (#324)

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## Pull Request type

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- [ ] Bugfix
- [x] Feature
- [ ] Code style update (formatting, renaming)
- [ ] Refactoring (no functional changes, no API changes)
- [ ] Build-related changes
- [ ] Documentation content changes
- [ ] Other (please describe):

## Description

This PR introduces a new Alexandria package, `alexandria_macros`. The
idea is to group any and all useful macros in here. As an introduction,
it also adds a humble `pow!` macro that calculates x to the power of y.
I hope many more will follow.

Because Cairo macros are Rust programs, I added a new separate GitHub
workflow just to test macros. Also because of the way macros work (at
least to my understanding), I added a `macros_tests` directory that
serves just as a dummy Scarb project to run tests on; it is not part of
the Alexandria workspace. Not sure this is the best way to go about it,
but having the tests inside the main macros package didn't work for me
(i.e. I didn't find a way how to do it, if there's some, I'm happy to
amend the PR).

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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---------

Co-authored-by: Marek Kaput <[email protected]>

.github/workflows/macros.yml

@@ -0,0 +1,53 @@
+name: Macros CI
+
+on:
+  push:
+    paths:
+      - 'packages/macros/**'
+      - 'packages/macros_tests/**'
+  pull_request:
+    paths:
+      - 'packages/macros/**'
+      - 'packages/macros_tests/**'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: packages/macros
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
+      - name: Build
+        run: cargo build --release
+
+  rustlint:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: packages/macros
+    env:
+      RUSTFLAGS: "-Dwarnings" # fail on warnings
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: clippy
+      - uses: Swatinem/rust-cache@v2
+      - name: Format check
+        run: cargo fmt --check
+      - name: Clippy
+        run: cargo clippy --all
+
+  scarbfmt:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: packages/macros_tests
+    steps:
+      - uses: actions/checkout@v4
+      - uses: software-mansion/setup-scarb@v1
+      - name: Cairo format check
+        run: scarb fmt --check

Scarb.lock

@@ -39,6 +39,10 @@ dependencies = [
  "alexandria_math",
 ]
 
+[[package]]
+name = "alexandria_macros"
+version = "0.1.0"
+
 [[package]]
 name = "alexandria_math"
 version = "0.2.1"

Scarb.toml

@@ -3,6 +3,7 @@ members = [
   "packages/data_structures",
   "packages/encoding",
   "packages/linalg",
+  "packages/macros",
   "packages/math",
   "packages/merkle_tree",
   "packages/numeric",