Add decrypted api for for box2 decrypted messages

[arj03]

This should fix #406

I went through a bit different solutions (see ssbc/jitdb#236), but ended up with a new pull source api.

I considered doing this so the operators could be reused, but decided against that because the filtering is often pretty simple and this also shows people that doing a filter on the result is not that scary. Where this could also be useful is if you have something like do a rough filter on post but then filter the result only for specific stuff without creating an index in jitdb.

[github-actions]

Benchmark results

Part	Duration
Create 5000 new messages	375.36ms
Validate 5000 messages	453.85ms
Native to db format 5000 messages	121.59ms
Db to native format 5000 messages	84.52ms
Add 1000 elements	487.80ms
Add 1000 box1 msgs	929.53ms
Unbox 1000 box1 msgs first run	214.18ms
Unbox 1000 box1 msgs second run	98.99ms
Add 1000 box1 msgs	893.36ms
Query 1000 msgs first run	37.49ms
Query 1000 msgs second run	21.09ms
Add 1000 box2 msgs	1291.75ms
Unbox 1000 box2 msgs first run	320.31ms
Unbox 1000 box2 msgs second run	149.18ms
Migrate (+db1)	11299.17ms
Migrate (alone)	3895.10ms
Migrate (+db1 +db2)	8275.14ms
Migrate (+db2)	6070.83ms
Migrate continuation (+db2)	918.66ms
Memory usage without indexes	753.86 MB = 42.46 MB + etc
Initial indexing	1628.30ms
Initial indexing maxcpu=86	5318.48ms
Initial indexing compat	771.83ms
Two indexes updating concurrently	2810.19ms
Key one initial	52.00ms
Key two	1.87ms
Key one again	2.04ms
Reboot and key one again	38.28ms
Latest root posts	1771.49ms
Latest posts	9.23ms
Votes one initial	1488.35ms
Votes again	0.56ms
HasRoot	1280.07ms
HasRoot again	0.37ms
Author one posts	1379.34ms
Author two posts	18.55ms
Dedicated author one posts	1435.46ms
Dedicated author one posts again	0.48ms
DeleteFeed	5721.17ms
Maximum memory usage	1018.56 MB = 56.37 MB + etc
Indexes folder size	10.01mb

[staltz]

Structurally looks good but I have a few suggestions for different approaches.

[arj03]

Should be ready to go now. Thanks for the review. I'll probably squash this as there is a bit too many commits. Happy with the result :)

[github-actions]

Benchmark results

Part	Duration
Create 5000 new messages	406.05ms
Validate 5000 messages	506.73ms
Native to db format 5000 messages	133.03ms
Db to native format 5000 messages	103.88ms
Add 1000 elements	552.10ms
Add 1000 box1 msgs	1040.07ms
Unbox 1000 box1 msgs first run	235.58ms
Unbox 1000 box1 msgs second run	111.83ms
Add 1000 box1 msgs	997.24ms
Query 1000 msgs first run	50.29ms
Query 1000 msgs second run	24.91ms
Add 1000 box2 msgs	1410.89ms
Unbox 1000 box2 msgs first run	376.88ms
Unbox 1000 box2 msgs second run	188.03ms
Migrate (+db1)	12872.16ms
Migrate (alone)	4553.32ms
Migrate (+db1 +db2)	9465.19ms
Migrate (+db2)	6907.56ms
Migrate continuation (+db2)	952.76ms
Memory usage without indexes	762.47 MB = 39.74 MB + etc
Initial indexing	1853.47ms
Initial indexing maxcpu=86	6008.02ms
Initial indexing compat	901.42ms
Two indexes updating concurrently	3182.26ms
Key one initial	55.15ms
Key two	0.53ms
Key one again	1.05ms
Reboot and key one again	47.52ms
Latest root posts	1960.77ms
Latest posts	10.63ms
Votes one initial	1604.99ms
Votes again	0.56ms
HasRoot	1428.01ms
HasRoot again	0.33ms
Author one posts	1543.71ms
Author two posts	16.75ms
Dedicated author one posts	1622.88ms
Dedicated author one posts again	0.61ms
DeleteFeed	6159.03ms
Maximum memory usage	1014.53 MB = 63.13 MB + etc
Indexes folder size	10.01mb

[staltz]

Looks good! Thanks

[github-actions]

Benchmark results

Part	Duration
Create 5000 new messages	575.98ms
Validate 5000 messages	583.60ms
Native to db format 5000 messages	169.19ms
Db to native format 5000 messages	120.32ms
Add 1000 elements	517.84ms
Add 1000 box1 msgs	1407.59ms
Unbox 1000 box1 msgs first run	326.96ms
Unbox 1000 box1 msgs second run	146.65ms
Add 1000 box1 msgs	1327.58ms
Query 1000 msgs first run	52.54ms
Query 1000 msgs second run	26.25ms
Add 1000 box2 msgs	2004.25ms
Unbox 1000 box2 msgs first run	557.11ms
Unbox 1000 box2 msgs second run	233.08ms
Migrate (+db1)	16563.72ms
Migrate (alone)	6035.07ms
Migrate (+db1 +db2)	12619.70ms
Migrate (+db2)	8808.96ms
Migrate continuation (+db2)	1493.48ms
Memory usage without indexes	749.56 MB = 42.68 MB + etc
Initial indexing	2142.62ms
Initial indexing maxcpu=86	6613.27ms
Initial indexing compat	1269.63ms
Two indexes updating concurrently	3986.64ms
Key one initial	65.65ms
Key two	1.06ms
Key one again	0.80ms
Reboot and key one again	69.51ms
Latest root posts	2449.03ms
Latest posts	11.62ms
Votes one initial	2025.21ms
Votes again	0.77ms
HasRoot	1849.02ms
HasRoot again	0.59ms
Author one posts	1948.42ms
Author two posts	22.35ms
Dedicated author one posts	2028.48ms
Dedicated author one posts again	0.68ms
DeleteFeed	7338.67ms
Maximum memory usage	1013.62 MB = 62.58 MB + etc
Indexes folder size	10.01mb