fix: explicitly set AllowNativePasswords=true in newDSN

[deanbaker]

Fixes #666

Problem

Spirit rejects connections to MySQL servers that use mysql_native_password authentication:

[mysql] could not use requested auth plugin 'mysql_native_password': this user requires mysql native password authentication
spirit: error: [MAIN-DATABASE-CONNECTION-FALLBACK] ping failed: this user requires mysql native password authentication

Root Cause

In newDSN() (pkg/dbconn/conn.go), Spirit explicitly sets several driver config options (RejectReadOnly, InterpolateParams, AllowCleartextPasswords) but does not explicitly set AllowNativePasswords. While NewConfig() defaults it to true, FormatDSN() omits default-true values from the DSN string, making the setting fragile across DSN serialization/deserialization cycles.

Fix

Explicitly set cfg.AllowNativePasswords = true in newDSN(), consistent with how other driver options are already configured.

Test

Added TestNewDSNAllowNativePasswords which validates AllowNativePasswords is true for both TLS-enabled (default PREFERRED mode) and TLS-disabled (fallback path) DSNs, and asserts the DSN never contains allowNativePasswords=false.

Also verified with integration test against a MySQL server using mysql_native_password:

• Baseline (no fix): could not use requested auth plugin 'mysql_native_password'
• Fixed: Connects successfully, proceeds to migration

[Copilot]

Pull request overview

This PR fixes Spirit’s inability to connect to MySQL instances using the mysql_native_password auth plugin by making newDSN() explicitly enable native password support, ensuring the setting survives DSN formatting/parsing behavior in go-sql-driver/mysql.

Changes:

• Explicitly set AllowNativePasswords=true on the MySQL driver config in newDSN().
• Add a unit test covering both TLS-enabled (default/PREFERRED) and TLS-disabled (fallback/DISABLED) DSN generation to ensure native passwords remain allowed.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pkg/dbconn/conn.go	Ensures newDSN() always enables AllowNativePasswords before formatting the DSN.
pkg/dbconn/conn_test.go	Adds coverage to validate AllowNativePasswords remains enabled across TLS and fallback DSNs.

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