ci: fix integration test skips and centralize core pattern

[anubhav756]

Description

Currently, the integration tests on Cloud Build suffer from regex evaluation and maintainability issues within .ci/integration.cloudbuild.yaml:

1. Core file and shared utility modifications (such as internal/util/parameters/parameters.go in fix: escape delimiter characters in applyEscape to prevent SQL injection #2811) skip many integration test shards because their PATTERN only looked for specific database source paths.
2. Shards like mysql and mssql used unanchored substring matching (mysql|), which accidentally triggered them whenever their Cloud SQL counterparts (cloudsqlmysql, cloudsqlmssql) were edited, leading to redundant/incorrect test runs.
3. Appending a massive core logic regex to 47 different shards creates a massive maintenance burden and violates DRY.

Changes

• Created a centralized .ci/core_pattern.txt file that contains core path regex (covering internal/server/, internal/util/, internal/auth/, etc.).
  • Every test shard now dynamically reads this via $$(cat .ci/core_pattern.txt), cleaning up the YAML file.
• Added Path Boundary Anchors (^|/) to all integration-specific regex terms (e.g., mysql is now (^|/)mysql/).
  • This eliminates substring leaks while preserving intentional file sharing (such as base postgres/ changes correctly triggering alloydb, alloydb-pg, and cloud-sql-pg shards).

Checklist

• Make sure to open an issue as a bug/issue before writing your code!
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)
• Make sure to add ! if this involves a breaking change

[gemini-code-assist]

Code Review

This pull request updates the file-change detection patterns across all 47 test shards in .ci/integration.cloudbuild.yaml to include additional core directories and files. The review feedback correctly points out a significant amount of duplication introduced by this change and suggests a maintainable, DRY alternative: writing the shared core pattern to a file in an initial step and reading it dynamically in each shard.