refactor: remove retired Options Strikes endpoint

[MarketDataDev03]

refactor: remove retired Options Strikes endpoint

Closes #20.

The standalone Options Strikes endpoint (GET /v1/options/strikes/{symbol}/) has been
retired — strikes data is now obtained via the chain endpoint. The docs already dropped the
strikes page (the API reference and the Python/PHP/Go SDK docs redirect /options/strikes →
/options/chain, and documentation@staging removed sdk/java/options/strikes.mdx). The Java SDK
still shipped the strikes() method, so it exposed a dead endpoint. This removes it.

Stacked on #18 (17_add_convinence_factory) — review/merge that first; this PR's base is that
branch, so the diff here is strikes-only.

Removed (strikes-endpoint only)

• OptionsResource — strikes(...) / strikesAsync(...) / strikesSpec(...), the
  OptionsStrikes deserializer registration, and now-unused imports
• OptionsCsvResource / OptionsHtmlResource — strikes() / strikesAsync()
• Classes: options/OptionsStrikesRequest, OptionsStrikesResponse, OptionsStrikesDeserializer,
  options/OptionsStrikes, options/ExpirationStrikes
• Tests: the strikes block in OptionsResourceTest (URL/params, decoding, envelope handling), the
  strikes assertions in the CSV/HTML facet coverage tests and RequestValidationTest, and
  OptionsIntegrationTest.strikesReturnsStrikesPerExpiration
• Docs: MarketDataClient javadoc, README.md, docs/OPTIONS_REVIEW_GUIDE.md

Kept (shared with chain — NOT part of the strikes endpoint)

• options/StrikeFilter and options/StrikeRange — used by OptionsChainRequest for the chain
  endpoint's strike filtering.

Testing

• ./gradlew build passes: unit tests, Spotless, and jacocoTestCoverageVerification
  (100% line coverage maintained).
• Repo-wide sweep confirms no remaining references to the removed endpoint
  (OptionsStrikes, ExpirationStrikes, .strikes(, strikesSpec, options/strikes).

Versioning

The SDK is pre-1.0 (0.x), so removing this endpoint is not a major/breaking bump under SemVer —
0.x explicitly allows API changes between minor releases. Bump the minor version (0.x → 0.(x+1)).

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