Improvement

[prozolic]

This PR change this following.

• Suppress inlining optimization on exception helper methods
• Improve out-of-bounds access safety using Debug.Assert and At extension methods
• Speed up decimal digit counting
• Optimize binary number parsing in TomlBinaryInteger
• Optimize UTF-8 conversion buffers size

[Copilot]

Pull request overview

This PR focuses on performance and safety-oriented internal optimizations across CsToml’s parsing/serialization pipeline, including numeric formatting/parsing, UTF-8 conversions, dictionary traversal, and exception helper behavior.

Changes:

• Adjust exception helper methods to discourage inlining, and introduce/expand debug-time bounds assertions via At(...).
• Optimize integer digit counting and binary integer parsing; update writer code paths to use the new digit counting routine.
• Tune UTF-8 conversion buffer sizing and apply small hot-path micro-optimizations (e.g., unsigned bounds checks).

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/CsToml/Values/TomlTableNodeDictionary.cs	Updates collision/bounds guards and enumerator null-handling in the internal table-node dictionary.
src/CsToml/Values/TomlInteger.cs	Optimizes binary integer parsing implementation.
src/CsToml/Values/TomlArray.cs	Minor formatting tweaks and unsigned bounds checks in enumerators.
src/CsToml/Utility/Utf8Helper.cs	Adjusts UTF-8 buffer sizing using Encoding.UTF8 helpers.
src/CsToml/Utility/SpanWriter.cs	Refactors SpanWriter storage/write logic (currently introduces a compilation issue).
src/CsToml/Utf8TomlDocumentWriter.cs	Switches digit counting calls to CountDigitsForInt64 and applies small formatting cleanups.
src/CsToml/TomlCodes.cs	Adds CountDigitsForInt64, uses At(...) for table lookups, and introduces whitespace byte spans (currently introduces a compilation issue).
src/CsToml/Extension/CollectionExtensions.cs	Implements At(...) with Debug.Assert bounds checks and unchecked access.
src/CsToml/Error/ExceptionHelper.cs	Changes throw helpers to [NoInlining] and fixes ThrowDeserializationFailed to include the message.

Comments suppressed due to low confidence (1)

src/CsToml/Values/TomlTableNodeDictionary.cs:178

• TryGetValueCore uses if ((uint)index > (uint)entries.Length) as an out-of-bounds guard, but index == entries.Length is already out of range and will fall through to entries[index]. Change the check to >= entries.Length to prevent potential out-of-range access when buckets/next pointers are corrupted.

        do
        {
            if ((uint)index > (uint)entries.Length)
            {
                value = null;
                return false;
            }

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