📐 Define a format-independent runtime fixed-angle contract

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Problem Statement

#2169 implements compile-time fixed-width OpenQASM angles and satisfies the representation and parser or lowering acceptance criterion in #1128. It intentionally lowers each folded angle to the existing binary64 gate-parameter boundary.

Runtime fixed-width angle state and device-aware angle quantization remain unresolved. Encoding either concern as OpenQASM-specific MLIR attributes would couple the compiler IR to one source format and create inconsistent behavior across importers and exporters.

Proposed Solution

Define a format-independent MLIR contract for runtime fixed-width angular values and target-aware quantization.

• Choose the owning dialect and representation for an angular value with a finite resolution.
• Define conversions between that representation and continuous floating-point gate parameters.
• Define the semantics of resizing, rounding, modular arithmetic, and runtime storage.
• Let compiler targets express supported angle resolutions and apply quantization at an explicit target-aware boundary.
• Extend OpenQASM runtime angle import and export only after the common representation exists.

The design must not add input-format-specific state to QC or QCO.

Acceptance criteria:

• A design note identifies the owning dialect, type or operation contract, and conversion boundaries.
• Tests cover runtime storage, conversion, and target-dependent quantization without depending on OpenQASM syntax.
• OpenQASM runtime angle declarations, reassignment, inputs, and outputs use the common contract when implemented.

This issue tracks the work that remains after #2169 closes #1128.