fix(parameters): add NBA Cup and IST season type constants (#620)

[parthashirolkar]

Summary

• Add nba_cup and ist constants to SeasonType parameter class
• Both values resolve to "NBA Cup" and "IST" respectively
• Inherited by all season type parameter classes
• Updated unit tests to validate new constants

Issue

Fixes #620

Background

Users reported that 'IST' season type works with PlayerGameLogs but not TeamDashLineups. The underlying issue was that these season types (NBA Cup/IST) were not available as named constants in the library, forcing users to use raw string literals.

Changes

• src/nba_api/stats/library/parameters.py: Added two new attributes to SeasonType base class
  • nba_cup = "NBA Cup"
  • ist = "IST"
• tests/unit/test_parameters.py: Updated 6 test functions to assert new attributes exist and have correct values

Testing

• All 460 unit tests pass
• Verified constants work with TeamDashLineups and PlayerGameLogs
• Tested both constant values and direct string values (backward compatible)

Usage Example

from nba_api.stats.endpoints import TeamDashLineups
from nba_api.stats.library.parameters import SeasonTypeAllStar

endpoint = TeamDashLineups(
    team_id=1610612739,
    season="2024-25",
    season_type_all_star=SeasonTypeAllStar.nba_cup,
    get_request=True
)

[swar]

awesome, this makes sense. could you please provide URLs here so we can prove that these parameters are valid?

It'll make it easier to verify on here and for us to play around with. I see no problems with this MR other than just confirming the new values.

[parthashirolkar]

@swar, thank you so much for spending the time to review! Just so I understand you correctly, do you mean URLs as in the constructed API calls to nba.com 's API that use this filter?