fix(difs): Use PROTECT for shared debug files

[szokeasaurusrex]

ProjectDebugFile.file can now be shared by multiple rows.

Update the Django relation from CASCADE to PROTECT so ORM deletes match the intended ownership model. Keep deleting the backing File as a best-effort cleanup step after deleting a ProjectDebugFile, but leave it in place when another ProjectDebugFile still references it.

This prepares us for #106947, where the solution will be to allow multiple ProjectDebugFiles to share a single File row.

The database should already reject deleting a referenced File; this change makes Django raise ProtectedError instead of relying on a DB-level failure path.

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/migrations/1051_protect_projectdebugfile_file.py

for 1051_protect_projectdebugfile_file in sentry

--
-- Alter field file on projectdebugfile
--
-- (no-op)

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/migrations/1052_protect_projectdebugfile_file.py

for 1052_protect_projectdebugfile_file in sentry

--
-- Alter field file on projectdebugfile
--
-- (no-op)

[github-actions]

Backend Test Failures

Failures on 32730b7 in this run:

tests/sentry/issues/escalating/test_escalating.py::TestEAPIsEscalating::test_eap_and_snuba_hourly_counts_match — log

tests/sentry/issues/escalating/test_escalating.py:365: in test_eap_and_snuba_hourly_counts_match
    assert snuba_count == eap_count == 6
E   assert 0 == 6

tests/sentry/issues/escalating/test_escalating.py::TestEAPIsEscalating::test_eap_and_snuba_past_counts_match_multiple_groups — log

tests/sentry/issues/escalating/test_escalating.py:423: in test_eap_and_snuba_past_counts_match_multiple_groups
    assert eap_counts[group_a.id] == 2
E   KeyError: 233

tests/sentry/issues/escalating/test_escalating.py::TestEAPIsEscalating::test_eap_hourly_count_excludes_old_events — log

tests/sentry/issues/escalating/test_escalating.py:382: in test_eap_hourly_count_excludes_old_events
    assert snuba_count == eap_count == 1
E   assert 0 == 1

tests/sentry/issues/escalating/test_escalating.py::TestEAPIsEscalating::test_eap_and_snuba_past_counts_match_single_group — log

tests/sentry/issues/escalating/test_escalating.py:396: in test_eap_and_snuba_past_counts_match_single_group
    assert len(snuba_results) == len(eap_results) == 1
E   assert 0 == 1
E    +  where 0 = len([])

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/migrations/1053_protect_projectdebugfile_file.py

for 1053_protect_projectdebugfile_file in sentry

--
-- Alter field file on projectdebugfile
--
-- (no-op)