Update TomlFloat and DecimalFormatter

[prozolic]

This PR change TomlFloat and DecimalFormatter process.

Change:

• TomlFloat: Utf8Parser.TryParse
• DecimalFormatter : TomlDocumentNode.TryGetDouble and Utf8TomlDocumentWriter.WriteDecimal

This change was created by Claude Code.

[Copilot]

Pull request overview

This PR updates numeric handling in CsToml by switching float parsing to Utf8Parser.TryParse and refactoring decimal serialization/deserialization to use TomlDocumentNode.TryGetDouble plus a new Utf8TomlDocumentWriter.WriteDecimal helper, with added test coverage for float boundaries and generated decimal types.

Changes:

• Update TomlFloat.Parse to use System.Buffers.Text.Utf8Parser.TryParse.
• Add Utf8TomlDocumentWriter.WriteDecimal and use it from DecimalFormatter / NullableDecimalFormatter.
• Add/extend tests for float boundary values and generator-driven decimal serialization/deserialization.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
tests/CsToml.Tests/DefaultTest.cs	Adds additional float boundary tests (max/min/epsilon, exponents, negative zero).
tests/CsToml.Generator.Tests/Generator/TypeDecimalTest.cs	New generator tests for decimal serialization/deserialization, including many edge cases.
tests/CsToml.Generator.Tests/Declarations/TypeDeclarations.cs	Adds a generated TypeDecimal model for generator tests.
src/CsToml/Values/TomlFloat.cs	Switches float parsing to Utf8Parser.TryParse.
src/CsToml/Utf8TomlDocumentWriter.cs	Adds WriteDecimal(decimal) implementation.
src/CsToml/Formatter/DecimalFormatter.cs	Refactors decimal formatter to deserialize via TryGetDouble and serialize via WriteDecimal.

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