[Repo Assist] Add AsyncSeq.transpose — mirror Seq.transpose for async sequences

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Summary

Adds AsyncSeq.transpose, a new combinator that mirrors [Seq.transpose]((fsharp.github.io/redacted) for async sequences.

Motivation

Seq.transpose is a useful utility for "rotating" a sequence of rows into a sequence of columns. This PR brings the same capability to AsyncSeq.

API

/// Transposes the rows and columns of an async sequence of sequences, yielding each
/// column as an array. Buffers the entire source sequence. Raises InvalidOperationException
/// if inner sequences have different lengths. Mirrors Seq.transpose.
val transpose : source:AsyncSeq(seq<'T)> -> AsyncSeq<'T[]>

Example:

let rows =
    asyncSeq {
        yield [| 1; 2; 3 |] :> seq(int)
        yield [| 4; 5; 6 |] :> seq(int)
    }
let cols = AsyncSeq.transpose rows |> AsyncSeq.toArrayAsync |> Async.RunSynchronously
// cols = [| [|1;4|]; [|2;5|]; [|3;6|] |]
```

## Implementation Notes

- Buffers all inner sequences to arrays first, then yields columns (same approach as `rev`).
- Raises `InvalidOperationException` with message `"The input sequences have different lengths."` for jagged inputs, matching `Seq.transpose` semantics.
- Placed under `#if !FABLE_COMPILER` (same as `rev`) since it depends on `toListAsync`.
- Accepts `AsyncSeq(seq<'T)>` so callers can pass `AsyncSeq<'T[]>`, `AsyncSeq(list<'T)>`, etc. with a coercion.

## Test Status

✅ **323/323 tests pass** (6 new `transpose` tests covering: basic 2×3 matrix, empty outer, single row, single column, singleton, and jagged-input error).

```
Passed! - Failed: 0, Passed: 323, Skipped: 0, Total: 323

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