feat!: Refactor initialisers

[ghaith]

This PR refactors the initial value generation for PLC application

• the init functions are removed and replaced with __ctor functions.
• initial constructors (__ctors) are created for every type and POU created in the current application
• external units are assumed to perform their own initialization.
• If an external type is used in a PLC application, the constructor functions are called at initialization
• A compilation flag was added to generate only the constructors (useful for external libraries written in C)
• A compilation flag was added to generate constructors for functions marked as {external} (used in the standard lib).
• Constructors are now part of the same compilation unit as the types they are constructing.

Review notes:
The bulk of this change is in the plc_lowering crate under the initializer.rs module.
Changes to the codegen and resolver were needed to fix issues where an initialzer code was not working in the body of a function.

After the main feature was done, i went through all open issues that mentioned init and tried to add a testcase for the specific issue and fix it. i tagged the issues fixed in this PR.
I split the commits into the main code change, the additional changes required to the pipeline and other componets, the new tests, documentation changes, some formatting changes and the insta tests.
I kept the changes in the snapshot isolated to one commit for easier review.

[Copilot]

Pull request overview

This PR refactors the initialization system within the compiler to move from explicit global initializer functions (__init__<name> and __user_init__<name>) to constructor-based initialization using LLVM's .init_array mechanism. The change consolidates init logic into a new plc_lowering::initializer module and introduces flags (--generate-external-constructors, --constructors-only) to control constructor generation for external libraries.

Changes:

• Replaced manual initializer generation with constructor functions (<Type>__ctor)
• Added linkage type Include to distinguish included files from external declarations
• Removed legacy vtable and init globals from stdlib Rust implementations
• Updated test snapshots to reflect filtered alignment values and removed init modules

Reviewed changes

Copilot reviewed 122 out of 618 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
compiler/plc_lowering/src/initializer.rs	New init lowering module implementing constructor generation
compiler/plc_driver/src/pipelines/participant.rs	Refactored InitParticipant to use new initializer
compiler/plc_ast/src/ast.rs	Added LinkageType::Include and helper methods
compiler/plc_llvm/	New crate with C++ wrapper to set LLVM UseInitArray option
libs/stdlib/src/timers.rs, libs/stdlib/src/flanks.rs, etc.	Removed manual vtable/init globals
libs/stdlib/tests/*	Updated test helpers to use includes + compile_and_load
compiler/plc_driver/src/cli.rs	Added --generate-external-constructors and --constructors-only flags
Snapshot files	Updated for alignment filtering and removed __initializers modules

Comments suppressed due to low confidence (1)

compiler/plc_lowering/src/initializer.rs:1

• The comment on line 4 in compiler/plc_lowering/src/tests/initializer_tests.rs contains a typo: 'aligment' should be 'alignment'.

//! The initializer lowering module is responsible for additing initialization logic

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[Copilot]

Corrected spelling of 'initialisers' to 'initializers' in the PR title for consistency with US English spelling used throughout the codebase.

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