feat: implement :perftrace and :help commands

[dlevy-msft-sql]

Summary

Adds the :perftrace command to redirect performance statistics output to a file, stderr, or stdout. This works in conjunction with the -p flag (PR #631) to control where timing statistics are written.

Syntax

sqlcmd -S server -Q "SELECT 1" -p
:perftrace <filename>|stderr|stdout

Changes

• pkg/sqlcmd/sqlcmd.go: Added stat writer field and GetStat/SetStat methods
• pkg/sqlcmd/commands.go: Added PERFTRACE command with file/stdout/stderr support
• pkg/sqlcmd/commands_test.go: Added tests for command parsing and functionality
• README.md: Added documentation with usage example

Testing

• All tests pass
• golangci-lint run passes (pre-existing warnings only)
• Build succeeds

Related

• PR feat: implement -p flag for print statistics #631 implements the -p flag for print statistics

[Copilot]

Pull request overview

This PR implements the :perftrace command to redirect performance statistics output to a file, stderr, or stdout, working in conjunction with the -p flag from PR #631.

Changes:

• Added stat writer infrastructure with GetStat/SetStat methods following the established pattern for output/error writers
• Implemented PERFTRACE command supporting file paths, "stdout", and "stderr" with variable substitution
• Added comprehensive test coverage for the command functionality

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
pkg/sqlcmd/sqlcmd.go	Added stat field and GetStat()/SetStat() methods for managing performance statistics output writer
pkg/sqlcmd/commands.go	Registered PERFTRACE command and implemented perftraceCommand() function with file/stdout/stderr support
pkg/sqlcmd/commands_test.go	Added TestPerftraceCommand() with comprehensive test scenarios and added PERFTRACE parsing tests
README.md	Documented the :perftrace command with usage example

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.