chore(bazel): add go_default_library alias for downstream naming compatibility

[roychying]

Why?

Some Bazel-based downstream consumers of this repo enforce their own naming convention where Go targets must be named go_default_library/go_default_test. When such a consumer uses our checked-in BUILD files directly (rather than regenerating them), our native target names don't satisfy that convention, so their consumer labels fail to resolve.

We need a fix that satisfies that requirement without renaming our own targets or breaking any other Bazel consumer relying on the native names.

This PR is addressing the same issue as #295 but use alias approach which is cheaper and less invasive.

What?

Adds # gazelle:go_naming_convention import_alias to the root BUILD.bazel and regenerates all BUILD files via make gazelle.

Test Plan

• make gazelle - clean; re-running make gazelle produces no further diff (idempotent).
• make build - all 337 targets build.
• make test - 65/65 tests pass, with hand-authored test targets keeping their original native names (e.g. buildsignal_test, not renamed to go_default_test).
• Verified consumption from a downstream Bazel workspace using this repo directly (checked-in BUILD files, no regeneration): with a local override pointed at this checkout, successfully built and tested downstream targets against the new go_default_library alias â�� confirming consumer labels resolve correctly end-to-end.

Issue

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[roychying]

Close this one. Adopt #295