feat: add native JSON type support for SQL Server 2025

[dlevy-msft-sql]

Adds native JSON type support for SQL Server 2025 Preview, enabling proper handling of the new JSON data type.

Features

• Add JSON token type (typeJson = 0xF4) and type parsing
• Add featureExtJsonSupport for TDS login negotiation
• Track JSON support capability in session state
• Sort feature extensions for deterministic login packets
• Comprehensive tests for JSON type scanning

Usage

JSON data is returned as string containing the JSON document. Supports scanning into:

• string
• []byte
• mssql.NullJSON (wraps json.RawMessage)
• Types implementing sql.Scanner

Requirements

• SQL Server 2025 Preview or later

---

Split from #306 for easier review

[Copilot]

Pull request overview

Adds end-to-end support for SQL Server 2025’s native JSON type, including TDS login feature negotiation, session capability tracking, JSON parameter declaration behavior with fallback, and tests/docs.

Changes:

• Introduces typeJson handling in TDS type parsing/metadata and SQL type name/decl generation.
• Adds featExtJSONSUPPORT negotiation in LOGIN7 and tracks jsonSupported on the session.
• Adds mssql.JSON / mssql.NullJSON parameter types plus a comprehensive JSON test suite and documentation updates.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
types.go	Adds JSON type ID, PLP decode path, and type metadata helpers (decl/name/length/prec-scale).
token.go	Parses server ACK payload for JSON feature extension.
tds.go	Adds JSON feature-ext request/ACK handling, session flag, and deterministic feature-ext ordering.
tds_login_test.go	Updates expected LOGIN7 hex blobs to include JSON feature extension and new deterministic ordering.
mssql_go19.go	Adds JSON/NullJSON types and parameter encoding with JSON-decl fallback logic.
mssql.go	Ensures JSON parameters are handled before driver.Valuer processing.
json_test.go	Adds unit + integration tests for JSON parameter behavior, fallback behavior, and declarations.
README.md	Documents JSON parameter types, compatibility/fallback behavior, and limitations.
CHANGELOG.md	Adds release note entry for JSON support.

[Copilot]

Pull request overview

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

[codecov-commenter]

Codecov Report

❌ Patch coverage is 85.81560% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.64%. Comparing base (c16a19e) to head (7e860f9).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
types.go	72.72%	9 Missing ⚠️
tds.go	70.37%	7 Missing and 1 partial ⚠️
mssql_go19.go	95.58%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #315      +/-   ##
==========================================
+ Coverage   75.36%   78.64%   +3.27%     
==========================================
  Files          34       34              
  Lines        6597     6728     +131     
==========================================
+ Hits         4972     5291     +319     
+ Misses       1337     1155     -182     
+ Partials      288      282       -6     

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[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 14 out of 17 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 14 out of 17 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 14 out of 17 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 14 out of 17 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 14 out of 17 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 14 out of 17 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 14 out of 17 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 14 out of 17 changed files in this pull request and generated no new comments.