nimble(serde): rename SerializationVersion::kTabletRaw to kTablet (#772)

[tanjialiang]

Summary:

Renames the kTabletRaw serialization format to kTablet across the nimble serde stack, plus all related identifiers, comments, and docs. The old kTabletRaw name created false symmetry with kCompactRaw — both ended in "Raw" but meant very different things: kCompactRaw is a regular serialization output using raw-encoded stream sizes, while kTabletRaw is a projection-only passthrough format with per-slice headers and chunk metadata preserved.

The rename signals "this is structurally different from the other formats" by breaking the parallel — the other names describe an encoding choice (Legacy, Compact, CompactRaw), while Tablet describes what the bytes are (passthrough tablet stream content).

This is a comment-and-name change only. The wire format byte stays 3 and on-disk/over-the-wire compatibility is preserved.

Identifier renames:

• SerializationVersion::kTabletRaw → SerializationVersion::kTablet
• isTabletRawFormat() → isTabletFormat() (both overloads)
• TabletRawChunkStripTest → TabletChunkStripTest (test class)
• serializeTabletRaw() → serializeTablet() (test helper)
• deserializeTabletRaw() / deserializeTabletRawWithDCtx() → deserializeTablet() / deserializeTabletWithDCtx() (test helpers)
• tabletRawVersionRejected, tabletRawDeserialization, Serializer_TabletRaw → tabletVersionRejected, tabletDeserialization, Serializer_Tablet (test names)
• "TabletRawFormat" test-parameter string → "TabletFormat"
• tabletRaw / tabletRawInput / tabletRawOwned local variables → tablet / tabletInput / tabletOwned
• "tablet_raw_chunk_test" memory pool name → "tablet_chunk_test"
• All comment and doc references to kTabletRaw / "tablet raw" updated to kTablet.
• Options.cpp::toString() returns "kTablet" to match the new enum name.
• Serializer.cpp error message updated: "kTablet is not supported by the serializer..."

Out of scope: the configerator-side thrift comment at configerator/structs/datainfra/joiner/sequence_storage_config.thrift:141 ("V3 (tabletRaw):") is an auto-generated mirror and must be updated from the configerator source repo in a separate diff.

Reviewed By: xiaoxmeng

Differential Revision: D106206709

[meta-codesync]

@tanjialiang has exported this pull request. If you are a Meta employee, you can view the originating Diff in D106206709.