fix(baseball): correct player position and free_agents position filter

[gdifiore]

Player.position used POSITION_MAP (lineup slot IDs) with a -1 offset to resolve defaultPositionId, causing wrong positions for nearly every player (e.g. Bryan Woo: C instead of SP). The two ID systems are unrelated — defaultPositionId=1 means SP, but lineup slot 0 is C.

• Fixes this by introducing DEFAULT_POSITION_MAP, which maps defaultPositionId directly to position strings.
• Also adds the missing reverse str→int entries to POSITION_MAP (previously # reverse TODO), enabling free_agents(position=...) to correctly filter by lineup slot ID. Without them, the position filter was silently ignored.

Reproducible PoC:

from espn_api.baseball import League

league = League(LEAGUE_ID, YEAR, espn_s2=ESPN_S2, swid=SWID)

# Bug 1: Player.position — pitchers show wrong position
pitchers = [p for team in league.teams for p in team.roster if p.lineupSlot == 'P']
print([p.position for p in pitchers[:3]])  # expected SP/RP

# Bug 2: free_agents(position=...) filter silently ignored
sps = league.free_agents(size=5, position='SP')
print([p.position for p in sps])  # expected all SP

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.09%. Comparing base (b4c6148) to head (40feee9).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #687      +/-   ##
==========================================
+ Coverage   71.06%   71.09%   +0.02%     
==========================================
  Files          62       62              
  Lines        2426     2425       -1     
==========================================
  Hits         1724     1724              
+ Misses        702      701       -1     

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[cwendt94]

Thanks for fixing this issue and adding unit tests!