[Repo Assist] feat: add LazyList.consLazy for constructing from Lazy(LazyList<'T)>

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Implements the enhancement requested in #134.

Summary

LazyList.consDelayed accepts unit -> LazyList<'T> (a thunk). When a Lazy(LazyList<'T)> value is already available, wrapping it in fun () -> tail.Value works but is unnecessarily wasteful — it allocates an extra closure and forgoes .NET's built-in Lazy caching.

consLazy provides the direct construction:

val consLazy : 'T -> Lazy(LazyList<'T)> -> LazyList<'T>

Usage example (infinite list of 1s, as shown in #134):

let rec ones: LazyList(int) = LazyList.consLazy 1 (lazy ones)

Implementation

let consLazy x (l: Lazy(LazyList<'T)>) =
    lzy(fun () -> consc x l.Value)

The outer lzy keeps the head cell lazy until the list is consumed. l.Value is the standard .NET Lazy(T) evaluation, which caches the result and is evaluated at most once.

Changes

• src/FSharpx.Collections/LazyList.fs — add consLazy
• src/FSharpx.Collections/LazyList.fsi — add signature + doc comment
• tests/FSharpx.Collections.Tests/LazyListTests.fs — 4 new tests: head access, toList, lazy divergence check (tail not evaluated on construction), and infinite list

Test Status

✅ All 710 tests pass (Passed: 710, Skipped: 6, Failed: 0). The 6 skipped tests are pre-existing skips unrelated to this change.

Related to #134

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