feat: add of(...) convenience factory to StockQuotesRequest and OptionsQuotesRequest

[MarketDataDev03]

feat: add of(...) convenience factory to StockQuotesRequest and OptionsQuotesRequest

Closes #17.

Every request type in the SDK exposes a paired construction surface — Foo.of(required...)
(convenience factory, required args only) and Foo.builder(required...) (full builder for
optionals). Two multi-symbol request types were missing the of(...) half and only had
builder(...):

• StockQuotesRequest
• OptionsQuotesRequest

Their varargs sibling StockPricesRequest already has both, so this was an accidental omission,
not a design choice — a consumer wanting a no-options multi-symbol quote was forced into
.builder(...).build() for no reason.

Changes

• StockQuotesRequest.of(String first, String... rest) — mirrors StockPricesRequest.of.
• OptionsQuotesRequest.of(String first, String... rest) — same.
• Each is a one-line shortcut for builder(first, rest...).build().
• Added unit tests in RequestValidationTest covering both factories (symbols carried, optionals
  default to null).

// before
client.stocks().quotes(StockQuotesRequest.builder("AAPL", "MSFT").build());
// after
client.stocks().quotes(StockQuotesRequest.of("AAPL", "MSFT"));

Testing

• ./gradlew build passes: unit tests, Spotless, and jacocoTestCoverageVerification
  (100% line coverage is maintained — the new factories are exercised by the added tests).

Motivation

The API-section docs in MarketDataApp/documentation#154
add Java/Kotlin examples for every endpoint. The multi-symbol quote examples were the only ones
that couldn't use the minimal .of(...) form because of this gap; once this ships they read as
cleanly as the rest.

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[MarketDataApp]

It looks good to me. This is what I wanted to see:

// before
client.stocks().quotes(StockQuotesRequest.builder("AAPL", "MSFT").build());
// after
client.stocks().quotes(StockQuotesRequest.of("AAPL", "MSFT"));

I'll defer to @MarketDataDev01 on the code review, however.