Cardano Updates

Keep the mask-interpretation logic out of the Sync service handlers. The
`BlockMask` strategy and its path parsing now live in `masking.rs` next to
`apply_mask`, with a module doc explaining when each applies: `apply_mask` is a
post-hoc JSON projection for low-volume Query responses, `BlockMask` is a
source-level projection for the high-volume Sync streams. The handlers only
extract the paths and consult the flags while building the version-specific
`AnyChainBlock`.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

The Sync service always populated both `native_bytes` and the fully parsed
chain block in every `AnyChainBlock`, ignoring the request's `field_mask`. A
consumer that needs only one representation transferred ~3.6x the data it used,
and the server always paid the cost of parsing the block even when only the raw
bytes were requested.

Honor `field_mask` on all three endpoints that return `AnyChainBlock`
(`DumpHistory`, `FetchBlock`, `FollowTip`) in both v1alpha and v1beta. The mask
gates work at the source: when the parsed block is masked out, `map_block_cbor`
is never called, and when `native_bytes` is masked out it is not copied. This
avoids the per-block CPU cost rather than just trimming the response, which is
why it does not reuse the JSON round-trip `apply_mask` used by the Query service.

Path matching is lenient and backwards compatible: an absent or empty mask
returns everything; a leading `block.` prefix (response-relative) is tolerated,
as are bare leaf names (`native_bytes`, `cardano`); selecting the whole `block`
field keeps both representations.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

The gRPC server built its tonic transport with no HTTP/2 tuning, inheriting
hyper/h2 defaults (64 KiB per-stream flow-control window, adaptive windowing
off) with no way for operators to influence them.

Add optional HTTP/2 fields to GrpcConfig (http2_adaptive_window,
http2_initial_stream_window_size, http2_initial_connection_window_size,
http2_max_frame_size, http2_max_concurrent_streams), all backwards-compatible
optional fields, and plumb them into the server builder via a dedicated
apply_http2_tuning helper.

Adaptive windowing defaults to on. NOTE: this is a behavior change for existing
deployments (windows now auto-size to the BDP instead of being pinned at
64 KiB). Adaptive and explicit fixed windows are mutually exclusive in hyper;
setting both logs a warning rather than silently dropping the fixed sizes.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>