Feature/allocate strings on heap

[Mauw94]

No description provided.

[Copilot]

Pull request overview

This PR moves runtime string values to heap-allocated HeapStringObject handles (via interning), and updates VM execution and stdlib native dispatch to work with heap-backed strings.

Changes:

• VM: push string constants as heap strings; build concatenation results as heap strings.
• VM: refactor heap allocations behind a helper (AllocateHeapObject).
• Stdlib native dispatcher: return/read/accept heap-allocated strings for File prelude APIs; enable parallel test execution for StdLib tests.

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
Lumi.VM/VirtualMachine.cs	Push constants/concats as heap strings; refactor heap allocations; adds string helpers.
Lumi.VM/Value.cs	Removes inline string payload from Value and updates constant/value printing logic.
Lumi.VM/NativeMemberDispatcher.cs	Updates File prelude methods to consume/produce heap strings and adjusts argument extraction.
Lumi.StdLib.Tests/MSTestSettings.cs	Enables method-level MSTest parallelization for StdLib tests.
Lumi.slnx	Changes solution build behavior for Lumi.VM.Heap.Tests in Debug configuration.
Lumi.Bytecode/Constants/ConstantPool.cs	Adds a TODO note about dead-constant cleanup after optimizations.

Comments suppressed due to low confidence (1)

Lumi.VM/Value.cs:65

• Value.PrintValue() no longer handles heap-allocated string values (they are now ValueKind.HeapObject). This means composite heap objects that print nested Values via Value.PrintValue() (e.g., HeapArrayObject.PrintValue() / HeapStructObject.PrintValue()) will now throw UnkownValueKind(HeapObject) when they contain strings (or any other heap values).

        ValueKind.Boolean => Bool.ToString(),
        ValueKind.Null => "null",
        ValueKind.Undefined => "undefined",
        _ => throw VirtualMachineError.UnkownValueKind(Kind),
    };

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