chore: give every coverage pragma a reason (TS6)

[lesnik512]

Brings the coverage pragmas in line with TS5 and TS6: every # pragma: no cover now carries its reason on the same line. exclude_also was already exactly ["if typing.TYPE_CHECKING:"] and no file is excluded, so TS5 needed no change.

Counts: 0 tested / 0 deleted / 4 reasoned.

• tests/test_inject.py: body of a method inject refuses to call without DIInterceptor.
• tests/test_aio.py (2): the coveragepy #2124 workaround; the multi-line comment above the two lines moves onto the pragmas, which is now where the reason lives.
• examples/app.py: the __main__ guard; tests call build_server() directly.

modern_di_grpc/main.py already had a reason (in parentheses) and is left untouched.

Local checks

• just install: ok
• just lint-ci: pass
• just test-ci: 37 passed, 100 % coverage