fix(sqlite3): support relative path for dbname

[KeitaShimura]

Summary

• Users can now specify a relative path (e.g. ./mydb.sqlite) for dbname in sqlboiler.toml
• In Assemble, the dbname is resolved to an absolute path via filepath.Abs() before building the connection string

Problem

When a relative path was given as dbname, SQLite resolved it against the working directory at the time of execution. Since the working directory when running sqlboiler differs from the one used when running generated tests, the same relative path pointed to different locations, causing no such table errors.

Changes

drivers/sqlboiler-sqlite3/driver/sqlite3.go

• Resolve dbname to an absolute path with filepath.Abs() if it is not already absolute

drivers/sqlboiler-sqlite3/driver/sqlite3_test.go

• Extract DB creation logic into a createSQLiteDB helper
• Add test cases for each path format:

Test case	Path format	Example	filepath.IsAbs()	Resolved by filepath.Abs()
absolute_path	Absolute path	/var/folders/.../mydb.sql	true (no-op)	-
relative_path	Relative path with ../	../../var/folders/.../mydb.sql	false	yes
relative_path_dot_slash	Relative path with ./	./mydb.sql	false	yes

Related issue

Related to #1409