Fully implement JSON binary writing, and add the ability to write directly from POCOs

[alex-clickhouse]

Adds POCO serialization for JSON columns with typed hints, allowing users to skip the JsonNode serialization when inserting from a POCO to a JSON column.

• POCOs serialize using ClickHouse binary encoding when column has type hints (e.g., JSON(Id Int64))
• Unhinted properties are auto-inferred and written as dynamic paths
• [ClickHouseJsonPath("path")] and [ClickHouseJsonIgnore] attributes control property to path mapping

Implementation:

• Single-pass buffered writing: we write to a buffer first, because we need to count the number of fields (and the number of fields comes before the actual data). Uses a memory pool for the buffer.
• Reflection results and type inference results are cached for perf.
• Nullable handling: Only writes nulls for hinted Nullable types (ClickHouse disallows Nullable in dynamic Variant paths)
• Case-sensitive matching: Matches ClickHouse behavior allowing userName and UserName as separate paths
• BinaryTypeEncoder: New encoder for writing type headers on dynamic paths

Breaking: String/JsonNode inputs now use string serialization (requires input_format_binary_read_json_as_string=1). First-class support for this will come in a different pr: #175 (There are some temporary hacks for the tests related to this).

---

Note

Introduces first-class JSON write support and Dynamic write capabilities.

• POCO → JSON binary write: New RegisterJsonSerializationType<T>() on ClickHouseConnection/IClickHouseConnection; attributes ClickHouseJsonPath and ClickHouseJsonIgnore; validation errors via ClickHouseJsonSerializationException; cached reflection and nested type handling via JsonTypeRegistry.
• JSON write behavior: string/JsonNode inputs are sent as JSON strings for server parsing (requires input_format_binary_read_json_as_string=1); hinted paths use column types; unhinted properties are inferred.
• Dynamic writes: Implemented DynamicType.Write with automatic type inference and new BinaryTypeDescriptionWriter for type headers.
• Type/mapping tweaks: Adjusted TypeSettings to carry registry; expose EnumType.Values; set default scale for Decimal128 mapping.
• Tests/notes: Extensive new tests for JSON registration/serialization and Dynamic round-trips; temporary skip of JSON samples in utilities; release notes updated.

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[codecov]

Codecov Report

❌ Patch coverage is 62.83988% with 123 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...kHouse.Driver/Types/BinaryTypeDescriptionWriter.cs	26.38%	118 Missing and 2 partials ⚠️
ClickHouse.Driver/Types/JsonType.cs	95.23%	1 Missing and 2 partials ⚠️

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[Copilot]

Pull request overview

This PR implements comprehensive POCO serialization for ClickHouse JSON columns, enabling type-safe binary encoding when column type hints are present. The implementation adds reflection-based property mapping with caching, attribute-based path customization, and automatic type inference for unhinted fields.

Changes:

• Adds POCO serialization with binary encoding for JSON columns using type hints from column definitions
• Implements BinaryTypeEncoder for writing ClickHouse type headers on dynamic paths
• Changes string/JsonNode inputs to use string serialization (requires input_format_binary_read_json_as_string=1)

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
RELEASENOTES.md	Documents breaking change for string/JsonNode JSON writing and new POCO serialization feature
ClickHouse.Driver/Types/JsonType.cs	Core implementation: adds reflection caching, POCO field writing, type inference, and binary encoding
ClickHouse.Driver/Types/EnumType.cs	Exposes Values dictionary as internal for BinaryTypeEncoder access
ClickHouse.Driver/Types/BinaryTypeEncoder.cs	New encoder that writes ClickHouse binary type headers for dynamic JSON paths
ClickHouse.Driver/PublicAPI/PublicAPI.Unshipped.txt	Adds public API surface for new JSON attributes
ClickHouse.Driver/Json/ClickHouseJsonPathAttribute.cs	New attribute for custom JSON path mapping
ClickHouse.Driver/Json/ClickHouseJsonIgnoreAttribute.cs	New attribute to exclude properties from serialization
ClickHouse.Driver.Tests/Utilities/TestUtilities.cs	Temporarily disables JSON data type samples pending full string format support
ClickHouse.Driver.Tests/Types/JsonTypeTests.cs	Comprehensive test coverage for POCO serialization scenarios
ClickHouse.Driver.Tests/BulkCopy/BulkCopyTests.cs	Updates existing tests with required server setting for string-based JSON parsing

[mzitnik]

Let's also write unhappy path tests

• wrong paths/types
• Empty values

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.