[Repo Assist] Fix JsonConversions.AsDecimal to handle JsonValue.Float

[github-actions]

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Closes #1230

Problem

When the JSON parser encounters a number in exponential notation (e.g. 3.45678E5), Decimal.TryParse with NumberStyles.Currency fails because Currency does not include AllowExponent. The value is therefore stored as JsonValue.Float instead of JsonValue.Number.

JsonConversions.AsDecimal previously only handled JsonValue.Number (and JsonValue.String), so any field inferred as decimal that received an exponential-notation value at runtime threw "Expecting a Decimal at '…', got …".

Concrete reproduction (from #1230):

type ExponentialDataTypes =
    JsonProvider(Sample = """{ "mydata": [ 1, 2.34567E5, 3.14 ] }""")

// Fails with: Expecting a Decimal at '/mydata[1]', got 345678
ExponentialDataTypes.Parse("""{ "mydata": [2, 3.45678E5, 9.01] }""")

Root Cause

1. Sample 2.34567E5 → Decimal.TryParse fails → stored as JsonValue.Float(234567.0)
2. 234567.0 is an integer-valued float in Int32 range → inferred as Integer in JsonInference.fs
3. 3.14 → JsonValue.Number(3.14M) → inferred as Decimal
4. [Integer, Integer, Decimal] unifies to Decimal
5. At runtime, 3.45678E5 → JsonValue.Float(345678.0) — AsDecimal returns None → exception

Fix

Add JsonValue.Float handling to JsonConversions.AsDecimal, mirroring the existing pattern in AsInteger / AsInteger64:

| JsonValue.Float f when not (Double.IsInfinity f) && not (Double.IsNaN f) ->
    try Some (decimal f) with :? OverflowException -> None

Test Status

• Build passes
• All 248 FSharp.Data.Tests pass (including new regression test)
• All 2841 FSharp.Data.Core.Tests pass (1 pre-existing network test fails due to environment proxy blocking `(www.google.com/redacted) — unrelated to this change)

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[alex-piccione]

1. Is this comment necessary?
2. Why the JsonProvider is not created in-line like in the other tests?

[alex-piccione]

Generated test has a huge comment that I'm not sure is required to stay in the code and is not following the code style of the other tests.