refactor(decode): split god-file into mdds/decode/{error,headers,transport,extract,cell,v3} + lift tdbe::time (refs #500)

[userFRM]

Summary

Wave 2 structural refactor of crates/thetadatadx/src/decode.rs (2177 LoC).
No public-API change; thetadatadx::decode::* paths are preserved via
pub use mdds::decode at the crate root. Eastern-time / DST primitives
become a canonical tdbe::time module reused by mdds, fpss latency, and
flatfiles.

Module surface

Old decode.rs lines	New module	Concern
12-73	mdds/decode/error.rs	DecodeError enum + observed_name diagnostic helper
75-142	mdds/decode/headers.rs	HEADER_ALIASES v3 <-> schema map + find_header lookup
330-409	mdds/decode/transport.rs	decompress_response / decode_data_table (zstd thread-local pool)
411-481	mdds/decode/extract.rs	extract_{number,text,price}_column projections
296-328, 501-694, 704-713, generated mod	mdds/decode/cell.rs	per-cell strict decoders (row_*) + macro-generated parser surface
715-1037	mdds/decode/v3.rs	hand-written v3 parsers + parse_iso_date/parse_time_text/calendar consts
144-294 (and tests)	crates/tdbe/src/time.rs	Eastern-time + DST primitives (lifted to canonical tdbe::time)

Lifted to tdbe::time

• eastern_offset_ms
• march_second_sunday_utc
• november_first_sunday_utc
• april_first_sunday_utc
• october_last_sunday_utc
• civil_to_epoch_days
• timestamp_to_ms_of_day
• timestamp_to_date

tdbe::latency now reuses these helpers, removing the duplicate civil-date
arithmetic that previously lived alongside the latency wrapper. Generator
templates (build_support/ticks/templates/parser/eod_{date,num,num64}.rs.tmpl)
updated to call tdbe::time::* directly.

Public API confirmation

Zero public surface change. thetadatadx::decode::{DecodeError, decompress_response, decode_data_table, extract_*_column, parse_*_ticks, parse_option_contracts_v3, parse_calendar_days_v3, CALENDAR_STATUS_*}
all resolve through pub use mdds::decode at the crate root. External
consumers (sdks/python/src/decode_bench.rs, crates/thetadatadx/benches/bench_decode.rs,
crates/thetadatadx/tests/test_decode_captures.rs) compile unchanged.

Versioning

• thetadatadx: 8.0.33 -> 8.0.34 (patch; structural refactor only)
• tdbe: 0.12.9 -> 0.12.10 (additive time module)

Test plan

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace (453 lib tests + 9 integration tests pass)
• cargo deny check
• cargo run -p thetadatadx --bin generate_sdk_surfaces --features config-file -- --check
• cargo check --manifest-path tools/mcp/Cargo.toml --locked
• cargo clippy --manifest-path tools/mcp/Cargo.toml --all-targets -- -D warnings
• cargo test --manifest-path tools/mcp/Cargo.toml --no-run
• cargo check --manifest-path tools/server/Cargo.toml --locked
• cargo check --manifest-path sdks/python/Cargo.toml --locked
• cargo check --manifest-path sdks/typescript/Cargo.toml --locked
• python3 scripts/check_version_sync.py

Refs #500.

[userFRM]

Closing — refolding all 4 Wave 2 god-file splits into a single PR per workflow discipline (one wave = one PR). Will reopen as a single coordinated commit covering decode + protocol + config + conditions.