RFR: 8371475: HttpClient: Implement CUBIC congestion controller [v3]

[Daniel Jeliński]

On Mon, 17 Nov 2025 15:24:13 GMT, Daniel Fuchs <dfuchs at openjdk.org> wrote:

>> It cannot overflow when used correctly (i.e. when packetBytes < congestionWindow, and congestionWindow < 2 * MAX_BYTES_IN_FLIGHT).
>
> if congestionWindow >= minimumWindow is an invariant, maybe we should assert it whenever we change congestionWindow.

Added the assertions in the base class.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28195#discussion_r2549222644