Implements Strava method for fetching activities and adds corresponding vertical

[aborem]

Closes #42

Some constraints with the Strava API:

• When you make the lowest tier Strava application, you're only allowed one authorized user at a time. If you apply for more permissions, you can have additional users.
• The single authorized user for the lowest tier can be anyone, it doesn't have to be the creator of the application.
• The interactions with the API (i.e., the types of requests and responses) are identical for any tier, so what I've written in this PR should work for tiers with more permissions too.

I also extract the OAuth2 Session GET request call into the base class for generalizability.

Sample response

[
    {
        "resource_state": 2,
        "athlete": {"id": 111, "resource_state": 1},
        "name": "Afternoon Run",
        "distance": 111,
        "moving_time": 111,
        "elapsed_time": 111,
        "total_elevation_gain": 0.0,
        "type": "Run",
        "sport_type": "Run",
        "workout_type": 0,
        "id": 14676384061,
        "start_date": "2025-06-02T20:47:04Z",
        "start_date_local": "2025-06-02T15:47:04Z",
        "timezone": "(GMT-06:00) America/Chicago",
        "utc_offset": -18000.0,
        "location_city": null,
        "location_state": null,
        "location_country": null,
        "achievement_count": 0,
        "kudos_count": 1,
        "comment_count": 0,
        "athlete_count": 1,
        "photo_count": 0,
        "map": {
            "id": "111",
            "summary_polyline": "111111111111",
            "resource_state": 2,
        },
        "trainer": false,
        "commute": false,
        "manual": false,
        "private": false,
        "visibility": "followers_only",
        "flagged": false,
        "gear_id": null,
        "start_latlng": [111.111, -111.111],
        "end_latlng": [111.111, -111.111],
        "average_speed": 111.111,
        "max_speed": 111.111,
        "has_heartrate": false,
        "heartrate_opt_out": false,
        "display_hide_heartrate_option": false,
        "elev_high": 111.111,
        "elev_low": 111.111,
        "upload_id": 111,
        "upload_id_str": "111",
        "external_id": "111-activity.fit",
        "from_accepted_tag": false,
        "pr_count": 0,
        "total_photo_count": 0,
        "has_kudoed": false,
    }
]

[lisad]

FYI if/when we get to generating documentation, the backtick looks for references - and I don't think params like 'uri' work as references so they cause errors

[aborem]

Good to know, thanks! Seems like double backticks is what I'm looking for. #52 for the future