Resolve merge conflicts with devel branch refactoring (#25423)

The PR branch had merge conflicts with `devel` due to a major compiler
refactoring that extracted type definitions from `compiler/ast.nim` into
a new `compiler/astdef.nim` file.

## Changes

- Resolved conflict in `compiler/ast.nim` by accepting `devel`'s
refactored structure
- Merged 763 commits from `devel` branch (commit range:
`ce6a345..b3273e7`)
- Preserved original PR changes removing deprecated symbols from
`lib/core/macros.nim`

The core PR functionality (removal of deprecated macros API since
v0.18.1) remains intact while incorporating the upstream AST
refactoring.

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.github/workflows/ci_docs.yml

@@ -45,7 +45,7 @@ jobs:
           - target: windows
             os: windows-latest
           - target: osx
-            os: macos-13
+            os: macos-15
 
     name: ${{ matrix.target }}
     runs-on: ${{ matrix.os }}