fix: lib lint type hints, update license year

[yanksyoon]

Applicable spec: N/A

Overview

Type hint the lib to pass linting.

Rationale

Pass linting tests.

Juju Events Changes

None.

Module Changes

None.

Library Changes

Added type hint.

Checklist

• [x] The charm style guide was applied
• [x] The contributing guide was applied
• [x] The changes are compliant with ISD054 - Managing Charm Complexity
• [x] The documentation is generated using src-docs
• [x] The documentation for charmhub is updated
• [x] The PR is tagged with appropriate label (urgent, trivial, complex)

[github-actions[bot]]

Test coverage for 694316f9f3b6665820f18f7cd13d3c971fe876b9

Name             Stmts   Miss Branch BrPart  Cover   Missing
------------------------------------------------------------
src/charm.py       473     30    188      6    93%   417->419, 547, 632-634, 638-643, 651-652, 660-661, 669-674, 693-695, 796-805, 819->844, 1079-1083, 1139, 1182->1218, 1200
src/helpers.py      10      0      2      0   100%
------------------------------------------------------------
TOTAL              483     30    190      6    93%

Static code analysis report

Run started:2024-01-19 14:10:21.365264

Test results:
    No issues identified.

Code scanned:
    Total lines of code: 3871
    Total lines skipped (#nosec): 2
    Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
    Total issues (by severity):
        Undefined: 0
        Low: 0
        Medium: 0
        High: 0
    Total issues (by confidence):
        Undefined: 0
        Low: 0
        Medium: 0
        High: 0
Files skipped (0):