Improve type hints for backends

[waketzheng]

Description

Improve type hints to reduce type:ignore

Motivation and Context

Improve type hint of tortoise/backends without changing any code logic

How Has This Been Tested?

make test

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[coveralls]

Pull Request Test Coverage Report for Build 9559961752

Details

• 38 of 45 (84.44%) changed or added relevant lines in 8 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.03%) to 89.023%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tortoise/backends/oracle/client.py	1	2	50.0%
tortoise/contrib/mysql/fields.py	0	1	0.0%
tortoise/backends/oracle/executor.py	2	7	28.57%

Totals
Change from base Build 9543663341:	-0.03%
Covered Lines:	5870
Relevant Lines:	6496

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9562810843

Details

• 38 of 45 (84.44%) changed or added relevant lines in 8 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.03%) to 89.023%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tortoise/backends/oracle/client.py	1	2	50.0%
tortoise/contrib/mysql/fields.py	0	1	0.0%
tortoise/backends/oracle/executor.py	2	7	28.57%

Totals
Change from base Build 9543663341:	-0.03%
Covered Lines:	5870
Relevant Lines:	6496

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9565173623

Details

• 38 of 45 (84.44%) changed or added relevant lines in 8 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.03%) to 89.023%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tortoise/backends/oracle/client.py	1	2	50.0%
tortoise/contrib/mysql/fields.py	0	1	0.0%
tortoise/backends/oracle/executor.py	2	7	28.57%

Totals
Change from base Build 9563237685:	-0.03%
Covered Lines:	5870
Relevant Lines:	6496

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9565355799

Details

• 38 of 45 (84.44%) changed or added relevant lines in 8 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.03%) to 89.024%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tortoise/backends/oracle/client.py	1	2	50.0%
tortoise/contrib/mysql/fields.py	0	1	0.0%
tortoise/backends/oracle/executor.py	2	7	28.57%

Totals
Change from base Build 9563237685:	-0.03%
Covered Lines:	5870
Relevant Lines:	6496

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 10194560214

Details

• 49 of 55 (89.09%) changed or added relevant lines in 9 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.02%) to 89.136%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tortoise/backends/oracle/client.py	2	3	66.67%
tortoise/backends/oracle/executor.py	2	7	28.57%

Totals
Change from base Build 10115140001:	-0.02%
Covered Lines:	5944
Relevant Lines:	6557

---

💛 - Coveralls

[waketzheng]

@abondar Only improve type hint, and does not change any code logic. Can this be accepted?