Clone each repository once when it ships several addons (closes #52)

[refaim]

Fixes #52.

A repository providing several addons was cloned and reinstalled once per addon, and the progress counter grew quadratically with the size of each repository group.

Changes

• get_addon_states — request remote state once per distinct (url, branch) instead of once per addon. fetch_states used to yield one RemoteState per duplicate request, and each of those was fanned out across every addon of the repository, giving Σ group_size² progress increments. The counter now runs 1/N..N/N.
• cmd_update — group the selected addons by (url, branch) and call install_addon once per repository. install_addon has always been repository-level: it clones once and installs every addon it finds.
• mygit.fetch_states — keep per-remote branches in an ordered set, so the module itself guarantees one RemoteState per (url, branch) regardless of how the caller builds the request list. One list_heads() call per distinct URL, as before.
• cmd_update — collapse identical per-repository errors into one line, so a broken repository with five addons no longer prints five identical messages.
• toc.find_addons — name an addon after its folder rather than the .toc stem. With the standard multi-TOC layout (DBM-Core.toc + DBM-Core-WOTLKC.toc) the suffixed file used to win purely because rglob sorts - before ., so the addon was installed into AddOns/DBM-Core-WOTLKC/, breaking ## Dependencies: DBM-Core resolution (WoW resolves dependencies by folder name) and orphaning SavedVariables. The folder name now wins whenever the folder actually ships a matching base .toc; otherwise the stem is kept so the installed folder always contains a loadable <Folder>.toc.
• install_addon — drop config entries whose addon has disappeared from the repository. Such entries can never advance their stored commit, so they stay outdated forever and pull a clone on every run. Detection scans the clone without the expansion filter, so an addon that merely does not match the current game version is never mistaken for a stale one. The folder is deleted only when its checksum still validates; a hand-edited folder is left in place with a warning and shows up as untracked.

Verification

Measured with the repositories from the issue — ElvUI-WotLK/ElvUI (2 addons), ElvUI_AddOnSkins, ElvUI_Enhanced, Bunny67/WeakAuras-WotLK (4 addons), Ascension-Addons/DeadlyBossMods (25 addons), Zendevve/OmniInv-WoW — 34 addons across 6 repositories:

	before	after
clones per update	34	6
installs	648	34
progress counter	648/34	34/34

The installed tree was checked afterwards: all 34 folders contain the <Folder>.toc the 3.3.5 client loads, no required dependency is unresolved, WeakAuras/Libs/** stays nested instead of being split into separate addons, and the installed files match the source repositories exactly.

209 tests pass (including the integration suite) with 100% line and branch coverage.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (9859ba6) to head (43e5e8f).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #53   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines          551       583   +32     
  Branches        88        97    +9     
=========================================
+ Hits           551       583   +32     

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