[Repo Assist] perf: avoid ToCharArray allocations in TextConversions, HtmlParser, HtmlCssSelectors, HtmlOperations

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Continues the series of allocation-reduction PRs (#1725, #1728, #1729, #1733) by eliminating remaining ToCharArray() calls that create unnecessary intermediate allocations.

Changes

TextConversions.RemoveAdorners (hotpath)

The slow path for removing currency/percentage adorners used ToCharArray() |> Array.filter, allocating two char arrays before creating the final string. Replaced with a StringBuilder loop that iterates the string directly (string is IEnumerable<char> in .NET):

// Before: two intermediate char[] allocations
String(value.ToCharArray() |> Array.filter (...))

// After: single StringBuilder, pre-allocated to value.Length
let sb = System.Text.StringBuilder(value.Length)
for c in value do
    if not (...) then sb.Append(c) |> ignore
sb.ToString()

This is called on every number/date parse attempt across CSV, JSON, and XML type inference.

HtmlParser — reversed-tag detection

The malformed-end-tag check (<li></il>) reversed a string via ToCharArray() |> Array.rev. Replaced with Array.init using direct index arithmetic — avoids ToCharArray() and a second array for the reversed result.

HtmlCssSelectors — three sites

• StartsWith active pattern: removed ToCharArray() and compared the char list directly against the string via Seq.compareWith (strings are IEnumerable<char>)
• TokenStr active pattern: s.ToCharArray() |> Array.toList → List.ofSeq s
• Tokenize method: cssSelector.ToCharArray() |> Array.toList → List.ofSeq cssSelector

HtmlOperations — CSS attribute selector

v.ToCharArray() |> Seq.skipWhile ... → v |> Seq.skipWhile ... (direct string enumeration)

Test Status

• ✅ dotnet test tests/FSharp.Data.Core.Tests/ — 2909 passed, 0 failed
• ✅ Formatted with Fantomas 7.0.1

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