Add Postgres case, cast operator and rebind support

[daniil-pankratov]

Hello @houqp !
Here is PR with various fixes as well as MacOS build in the pipeline :)

• Added fix for Postgres cast operator ::;
• Added pass-through functions support such as Rebind/Rebindx in sqlx;
• Added Postgres CASE support;

[Copilot]

Pull request overview

This PR enhances PostgreSQL query support in sqlvet by adding CASE expression parsing, PostgreSQL cast operator (::) handling, and pass-through function support (like Rebind/Rebindx in sqlx). It also includes code quality improvements and macOS CI build support.

• Added PostgreSQL CASE expression parsing to handle conditional logic in queries
• Added support for pass-through functions like Rebind/Rebindx that transform query syntax
• Fixed handling of PostgreSQL cast operator (::) by only applying named query compilation to Named* functions

Reviewed changes

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

Show a summary per file

File	Description
pkg/vet/vet.go	Added CASE expression parsing logic to handle WHEN/THEN/ELSE clauses
pkg/vet/gosource_test.go	Added tests for Rebind support and PostgreSQL cast operators, replaced deprecated ioutil calls with os functions
pkg/vet/gosource.go	Implemented pass-through function detection, enhanced query string extraction, refactored to use constants, fixed error message capitalization
main.go	Version bump to 1.1.11
.github/workflows/build.yml	Added macOS to build matrix

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