attach #valtype to more types and expose Coroutine struct fields

[bobzhang]

Note this is not plan to be merged.

I am thinking we need an attribute like

#allow_in_valtype
struct Coroutine {
   ...
}

cc @Yu-zh

Summary

This PR extends the use of #valtype to more types and exposes additional struct fields in the public API.

Changes

• Task[X] — Added #valtype, enabling the struct to be passed as values (two reference fields: value: Ref[X?] and coro: Coroutine)
• Cond (cond_var) — Added #valtype; this struct has a single non-mutable field (waiters: Deque) so it qualifies
• Coroutine (internal/coroutine) — Changed from opaque type Coroutine to pub struct Coroutine, exposing its fields (coro_id, state, shielded, cancelled, ready, downstream) for downstream use and reflection
• State enum — Removed priv so it is accessible as part of the public Coroutine struct definition
• Regenerated pkg.generated.mbti for the coroutine package

Why not more types?

Several candidates were evaluated but cannot be #valtype due to language constraints:

• Semaphore, Queue[X] — have mut fields; #valtype disallows mutable fields
• Tcp, TcpServer, UdpClient, UdpServer, RawFd — all hold a @event_loop.IoHandle field which is an abstract type; #valtype disallows abstract type fields

Testing

moon check passes with no errors.

[coveralls]

Coverage Report for CI Build 312

Coverage remained the same at 79.202%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	4183
Covered Lines:	3313
Line Coverage:	79.2%
Coverage Strength:	59549.82 hits per line

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💛 - Coveralls

[Guest0x0]

If the intention of making Coroutine pub is to embed it in other value types, the fields should be made priv for the sake of minimal change, though.