Add optional RelationNature to TeamRelation with override; add tests

[ez-plugins]

Added

• Optional RelationNature enum (FRIENDLY, NEUTRAL, HOSTILE) to the model
  package. Each TeamRelation constant carries a built-in default nature which may
  be queried with getDefaultNature().
• Consumer override support: TeamRelation#setNatureOverride(RelationNature) and
  TeamRelation#getNature() — allows server or provider code to re-categorise a
  relation at runtime. Passing null to setNatureOverride clears the override
  and restores the builtin default. Overrides are visible JVM-wide because enum
  constants are singletons.
• Unit tests: TeamRelationTest covering default natures and override behaviour.

Changed

• TeamsAPI.API_VERSION bumped to 2.1.0.

Migration

No behavioural changes to existing TeamRelation helpers: isFriendly() and
isHostile() remain unchanged and existing consumers require no changes. Providers
that wish to reclassify relations (for example treating TRUCE as NEUTRAL) may
call setNatureOverride(...) during initialisation.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...com/skyblockexp/teamsapi/model/RelationNature.java	87.50%	1 Missing ⚠️

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