introduce new runners: unit-perf and use them for benchmark jobs (#11409)

## Problem
Benchmarks results are inconsistent on existing small-metal runners

## Summary of changes
Introduce new `unit-perf` runners, and lets run benchmark on them.

The new hardware has slower, but consistent, CPU frequency - if run with
default governor schedutil.
Thus we needed to adjust some testcases' timeouts and add some retry
steps where hard-coded timeouts couldn't be increased without changing
the system under test.
-
[wait_for_last_record_lsn](6592d69a67/test_runner/fixtures/pageserver/utils.py (L193))
1000s -> 2000s
-
[test_branch_creation_many](https://github.com/neondatabase/neon/pull/11409/files#diff-2ebfe76f89004d563c7e53e3ca82462e1d85e92e6d5588e8e8f598bbe119e927)
1000s
-
[test_ingest_insert_bulk](https://github.com/neondatabase/neon/pull/11409/files#diff-e90e685be4a87053bc264a68740969e6a8872c8897b8b748d0e8c5f683a68d9f)
- with back throttling disabled compute becomes unresponsive for more
than 60 seconds (PG hard-coded client authentication connection timeout)
-
[test_sharded_ingest](https://github.com/neondatabase/neon/pull/11409/files#diff-e8d870165bd44acb9a6d8350f8640b301c1385a4108430b8d6d659b697e4a3f1)
600s -> 1200s

Right now there are only 2 runners of that class, and if we decide to go
with them, we have to check how much that type of runners we need, so
jobs not stuck with waiting for that type of runners available.

However we now decided to run those runners with governor performance
instead of schedutil.
This achieves almost same performance as previous runners but still
achieves consistent results for same commit

Related issue to activate performance governor on these runners
https://github.com/neondatabase/runner/pull/138

## Verification that it helps

### analyze runtimes on new runner for same commit

Table of runtimes for the same commit on different runners in
[run](https://github.com/neondatabase/neon/actions/runs/14417589789)

| Run | Benchmarks (1) | Benchmarks (2) |Benchmarks (3) |Benchmarks (4)
| Benchmarks (5) |
|--------|--------|---------|---------|---------|---------|
| 1 | 1950.37s | 6374.55s |  3646.15s |  4149.48s |  2330.22s | 
| 2 | - | 6369.27s |  3666.65s |  4162.42s |  2329.23s | 
| Delta % |  - |  0,07 %  | 0,5 %   |   0,3 % | 0,04 %   |
| with governor performance | 1519.57s |  4131.62s |  - | -  |  - |
| second run gov. perf. | 1513.62s |  4134.67s |  - | -  |  - |
| Delta % |  0,3 % |  0,07 %  |  -  |  - | -   |
| speedup gov. performance | 22 % |  35 % |  - | -  |  - |
| current desktop class hetzner runners (main) | 1487.10s | 3699.67s | -
| - | - |
| slower than desktop class | 2 % |  12 % |  - | -  |  - |


In summary, the runtimes for the same commit on this hardware varies
less than 1 %.

---------

Co-authored-by: BodoBolero <peterbendel@neon.tech>

.github/workflows/build_and_test.yml

@@ -284,7 +284,7 @@ jobs:
       statuses: write
       contents: write
       pull-requests: write
-    runs-on: [ self-hosted, small-metal ]
+    runs-on: [ self-hosted, unit-perf ]
     container:
       image: ${{ needs.build-build-tools-image.outputs.image }}-bookworm
       credentials: