Allow Reading from Hint Space for MULTI_OBSERVE

[darth-cy]

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[Copilot]

Pull request overview

This PR extends the MULTI_OBSERVE Poseidon2 instruction to optionally read input data from hint space instead of memory. Previously, MULTI_OBSERVE always read input elements from a memory array pointer. Now, a context array is used to pass parameters (init_pos, len, is_hint, reserved), and when is_hint=1, data is read from hint space via the hint bus instead of memory.

Changes:

• Replaced separate init_pos and len register parameters with a context array (ctx_ptr) and added a hint_id register parameter across the entire instruction pipeline (compiler IR, ASM, conversion, execution, AIR, columns).
• Added conditional hint space lookup in the AIR constraints and trace generation: in hint mode, memory reads are skipped and hint bus lookups are used instead, with adjusted timestamp increments (1 per element instead of 2).
• Wired HintSpaceProviderChip into NativePoseidon2Filler to register hint bus interactions during trace filling.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
extensions/native/recursion/src/challenger/duplex.rs	Pass None for new hint_id parameter
extensions/native/compiler/src/ir/poseidon.rs	Allocate context array, pack params, read back result
extensions/native/compiler/src/ir/instructions.rs	Update Poseidon2MultiObserve variant to use ctx_ptr and hint_id
extensions/native/compiler/src/conversion/mod.rs	Update instruction field mapping for conversion
extensions/native/compiler/src/asm/instruction.rs	Update ASM instruction docs and display
extensions/native/compiler/src/asm/compiler.rs	Update DslIr→AsmInstruction mapping
extensions/native/circuit/src/poseidon2/execution.rs	Read ctx array and hint data in execution path
extensions/native/circuit/src/poseidon2/columns.rs	Add ctx array, read_ctx, register columns; remove old fields
extensions/native/circuit/src/poseidon2/chip.rs	Add hint_space_provider, conditional hint reads in trace gen
extensions/native/circuit/src/poseidon2/air.rs	Add hint bus lookups, conditional memory reads, timestamp adjustments
extensions/native/circuit/src/extension/mod.rs	Reorder chip creation to pass hint_space_provider to poseidon2
extensions/native/circuit/cuda/src/poseidon2.cu	Update CUDA trace fill for hint mode timestamps and reads

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