ClientEffectiveStrategyTest and ServerEffectiveStrategyTest cleanups (#1667)

* `ClientEffectiveStrategyTest` cleanups
Motivation:
The parameterization pattern used for `ClientEffectiveStrategyTest`
makes it difficult to understand the configuration under test because
it is built imperatively rather than as a set of declarative options.
Some refactoring
Modifications:
Restructured test parameterization. One specific case is improved; for
the cases where no offloading to provided executor is to be performed
the test now explicitly ensures that the test fails if the executor is
used.
Result:
Easier to understand test with easier to understand test cases.

Author: bondolo

servicetalk-http-api/src/main/java/io/servicetalk/http/api/StrategyInfluencerChainBuilder.java

@@ -50,7 +50,6 @@ private StrategyInfluencerChainBuilder(Deque<HttpExecutionStrategyInfluencer> in
      * Adds the passed {@link HttpExecutionStrategyInfluencer} to the head of this chain.
      *
      * @param influencer {@link HttpExecutionStrategyInfluencer} to add.
-     * @throws IndexOutOfBoundsException If the passed index is invalid.
      */
     public void prepend(HttpExecutionStrategyInfluencer influencer) {
         influencers.addFirst(requireNonNull(influencer));
@@ -62,7 +61,6 @@ public void prepend(HttpExecutionStrategyInfluencer influencer) {
      *
      * @param mayBeInfluencer An object which may be an {@link HttpExecutionStrategyInfluencer}.
      * @return {@code true} if the passed {@code mayBeInfluencer} was added to the chain.
-     * @throws IndexOutOfBoundsException If the passed index is invalid.
      */
     public boolean prependIfInfluencer(Object mayBeInfluencer) {
         if (mayBeInfluencer instanceof HttpExecutionStrategyInfluencer) {