[kaihsin]

Summary

With program-image-execution enabled, the CPU's Span and Breakpoint instructions are compiled out, and ExecutionState had no replacement for them. This PR adds both to the program dialect.

• program::breakpoint suspends the invocation after the instruction. execute/resume return Ok(()) with the new ExecutionState::is_paused() set, and pc() points at the following instruction. The next resume clears the pause and continues from there.
• A paused invocation is still active (not halted). start/execute and Loadable::replace_image are rejected until it completes or reset() is called, which also clears the pause.
• program::span file start end records a source span on the current frame, readable through ExecutionState::span(). Callee frames start at (0, 0, 0) and returning restores the caller's span.

The execute/resume return types are unchanged (eyre::Result<()>), so this change is not breaking. Callers check is_paused() to tell a breakpoint from completion.

Test plan

• New integration tests in crates/vihaco-stdlib/tests/execution_integration.rs: pause/resume at breakpoints, rejection of re-entry while paused, reset, and span recording and restoration across call/return
• cargo fmt --all -- --check
• cargo clippy in the default and vihaco/program-image-execution configurations
• cargo test --workspace --all-targets and --doc
• cargo test --workspace --exclude vihaco-doctests --all-targets --features vihaco/program-image-execution: all pass except the trybuild fixture vihaco-runtime/tests/compile_fail/dialect/out-of-line.rs, which fails the same way on main (unrelated to this PR)

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[Copilot]

🟢 Approval recommended

There are no active review issues blocking the breakpoint suspension and per-frame source-span changes.

No open issues 🎉

What changed in this PR

Adds breakpoint suspension and per-frame source spans to the program dialect for program-image execution, replacing capabilities unavailable from the CPU in this mode.

Changes:

• Adds breakpoint with pause/resume behavior and an is_paused() accessor, without changing runner return types.
• Adds span recording and inspection, with fresh spans for callees and restoration on return.
• Documents the behavior and adds integration tests for pauses, re-entry rejection, reset, and span tracking.

File	Description
README.md	Documents breakpoint and source-span behavior.
crates/​vihaco-stdlib/​tests/​execution_integration.rs	Tests pause/resume, reset, re-entry rejection, and frame spans.
crates/​vihaco-stdlib/​src/​program/​dialect.rs	Defines Breakpoint and Span instructions.
crates/​vihaco-stdlib/​src/​loadable.rs	Documents paused invocation restrictions and resumption.
crates/​vihaco-stdlib/​src/​execution_state/​storage.rs	Exposes pause/span accessors and clears pauses on start/reset.
crates/​vihaco-stdlib/​src/​execution_state/​runner.rs	Stops execution at breakpoints and clears pauses on resume.
crates/​vihaco-stdlib/​src/​execution_state/​execution.rs	Implements breakpoint and span instruction execution.
crates/​vihaco-stdlib/​src/​execution_state.rs	Adds pause state with default and clone support.

_{Review effort: Balanced}