Real session tracking, date densify, and a 100% pymongo gauge
Summary: Logical sessions are now real server-side state, $densify walks date ranges by week / day / hour / minute / second / millisecond, and the pymongo conformance gauge moves to a clean 100.0% (v0.3.0a77).
startSession / endSessions / refreshSessions are no longer no-op stubs. A new thread-safe secantus.sessions.SessionRegistry tracks logical sessions with a 30-minute idle TTL matching mongod's logicalSessionTimeoutMinutes, and any command that arrives carrying an lsid triggers implicit registration just like a real server. Drivers that lean on session housekeeping for retryable writes now see consistent state instead of a black hole.
$densify grew real date support: unit: "week" | "day" | "hour" | "minute" | "second" | "millisecond" all walk ranges in fixed-length increments, while variable-length units (month, quarter, year) reject with a clear error rather than silently producing wrong rows. Alongside that, hostInfo and whatsmyuri now return real values (hostname, OS, CPU arch, RAM, real connection peer) instead of placeholders, and $dateToString handles the mongod-specific %w token (1-Sun … 7-Sat) plus confirms %G / %V / %j / %U / %u match mongod 1:1.
The pymongo conformance gauge moves to 100.0%. The previous 99.5% was a report-generator bug where pytest-subtests was writing "subtests passed" lines that the parser miscounted as errors — every category was always green when run, the report just lied about it. Every line now correctly reads green.