[Feature] Return typed results (std::expected) from fallible mutators instead of silent logging

[Jgocunha]

What would you like?

Make fallible operations report failure to the caller — via std::expected<void, ErrorCode>
(or a returned status enum) — instead of logging an error and returning void, so callers and
the GUI can react to failures.

Use case / motivation

Several mutators validate, log on failure, and silently return:

// src/elements/element.cpp:43-77
void Element::addInput(const std::shared_ptr<Element>& inputElement, const std::string& inputComponent)
{
    if (!inputElement) { log(LogLevel::ERROR, "Input is null."); return; }   // caller can't tell
    ...
    if (sizes mismatch)  { log(LogLevel::ERROR, "...different size..."); return; }
}

When a user wires two incompatible elements in the node graph, the connection silently doesn't
happen and the only feedback is a line in the log window. The same pattern appears in
removeInput, createInteraction, and parts of file load. There's a well-structured
ErrorCode enum (include/exceptions/exception.h) already available to describe failures.

What's missing today?

No std::expected/std::optional on these APIs; success/failure isn't observable at the call
site. Error handling is split between exceptions (for "hard" errors) and log-and-continue (for
wiring/validation), inconsistently.

Possible approach

• Change the fallible mutators to return std::expected<void, ErrorCode> (C++23; available on
  the toolchains in use — GCC 13 / recent Clang / MSVC; verify and gate if needed) or, if
  C++23 <expected> isn't acceptable yet, return the existing ErrorCode enum.
• Keep logging for diagnostics, but let callers branch on the result. Update the node-graph
  connection code to surface a user-visible message / reject the link when addInput fails.
• Roll out incrementally (one API at a time), keeping behavior backward-compatible where
  callers ignore the result ([[nodiscard]] encourages handling).

Verifiable end state: addInput/removeInput/createInteraction (at minimum) return a
typed result; the node-graph UI reacts to failed connections instead of silently dropping them;
existing tests updated. Higher-risk Phase 3 item — stage per-API.