refactor!: move go-chi/session into Gitea (#39504)

The `gitea.com/go-chi/session` package only exists for Gitea, so it
moves into `modules/session` to fix its bugs directly. Fixes the flake
in
https://github.com/go-gitea/gitea/actions/runs/36726154500/job/109923538400.

- Sessions are only written back when changed, so a read-only request
can't revert a concurrent change or restore a logged-out session, like
https://github.com/go-macaron/session/commit/ae808a4a4660c802965c834299ab08f167effd12
- The session cookie is only set once a session holds data
- Every backend refreshes the expiry on load and file sessions are
written atomically
- Also fix  https://github.com/go-gitea/gitea/issues/36176

## ⚠️ BREAKING ⚠️

* the `mysql`, `postgres`, `couchbase` and `memcache` session providers
are removed, use `file`, `db` or `redis` instead
* login-related cookies are renamed to `gitea_session` and
`gitea_remember`, if you'd like to use the old names, set `COOKIE_NAME`
and `COOKIE_REMEMBER_NAME` in app.ini

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

go.mod

@@ -6,7 +6,6 @@ toolchain go1.27.1
 
 require (
 	connectrpc.com/connect v1.21.0
-	gitea.com/go-chi/session v0.0.0-20260708011333-ebced8a7a2d6
 	gitea.com/lunny/dingtalk_webhook v0.0.0-20171025031554-e3534c89ef96
 	gitea.com/lunny/levelqueue v0.4.2-0.20230414023320-3c0159fe0fe4
 	gitea.dev/actionslib v1.2.1
@@ -152,9 +151,6 @@ require (
 	github.com/clipperhouse/displaywidth v0.11.0 // indirect
 	github.com/clipperhouse/uax29/v2 v2.7.0 // indirect
 	github.com/cloudflare/circl v1.6.3 // indirect
-	github.com/couchbase/go-couchbase v0.1.1 // indirect
-	github.com/couchbase/gomemcached v0.3.4 // indirect
-	github.com/couchbase/goutils v0.3.0 // indirect
 	github.com/cpuguy83/go-md2man/v2 v2.0.7 // indirect
 	github.com/cyphar/filepath-securejoin v0.6.1 // indirect
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
@@ -175,7 +171,6 @@ require (
 	github.com/golang-sql/sqlexp v0.1.0 // indirect
 	github.com/golang/groupcache v0.0.0-20241129210726-2c02b8208cf8 // indirect
 	github.com/golang/snappy v1.0.0 // indirect
-	github.com/google/flatbuffers v25.12.19+incompatible // indirect
 	github.com/google/go-querystring v1.2.0 // indirect
 	github.com/google/go-tpm v0.9.8 // indirect
 	github.com/google/uuid v1.6.0 // indirect