fix(bake): don't mangle temp image name for registries with a port

[ianpittwood]

Problem

BakeTarget.from_image_target() stripped what it assumed was a tag off the temp image name with rsplit(":", 1)[0]. That split on the last : anywhere in the reference — including a registry port — so a --temp-registry with a port produced garbage:

"localhost:5000/package-manager/tmp".rsplit(":", 1)[0] == "localhost"

The bake target got tagged localhost, poisoning the resulting image.name metadata (and everything bakery ci publish derives from it) while the build still succeeded silently.

ImageTarget.temp_name returns {temp_registry}/{image}/tmp with no tag, so the rsplit was a no-op in every correct case — it could only ever do harm — and it made the bake strategy disagree with ImageTarget.build(), which uses temp_name verbatim.

Fix

Drop the rsplit; use image_target.temp_name directly, matching ImageTarget.build().

Tests

• test_temp_registry_with_port_not_mangled — --temp-registry localhost:5000 yields tag localhost:5000/test-image/tmp.
• test_temp_name_matches_build_strategy — bake tag equals ImageTarget.temp_name, proving bake/build produce the same image.name.

Fixes #738

[github-actions]

Test Results

2 246 tests   2 246 ✅  9m 21s ⏱️
    1 suites      0 💤
    1 files        0 ❌

Results for commit 7450d73.