Merge bitcoin/bitcoin#29608: optimization: Preallocate addresses in GetAddr based on nNodes

66082ca Preallocate addresses in GetAddr based on nNodes (Lőrinc)

Pull request description:

  The reserve method optimizes memory allocation by preallocating space for the expected number of elements (nNodes), reducing reallocations and improving performance. The upper bound ensures efficient memory usage based on the input constraints.

  before:
  ```
  |               ns/op |                op/s |    err% |     total | benchmark
  |--------------------:|--------------------:|--------:|----------:|:----------
  |           76,852.79 |           13,011.89 |    0.4% |      1.07 | `AddrManGetAddr`
  |           76,598.21 |           13,055.14 |    0.2% |      1.07 | `AddrManGetAddr`
  |           76,296.32 |           13,106.79 |    0.1% |      1.07 | `AddrManGetAddr`
  ```

  after:
  ```
  |               ns/op |                op/s |    err% |     total | benchmark
  |--------------------:|--------------------:|--------:|----------:|:----------
  |           65,966.97 |           15,159.10 |    0.3% |      1.07 | `AddrManGetAddr`
  |           66,075.40 |           15,134.23 |    0.2% |      1.06 | `AddrManGetAddr`
  |           66,306.34 |           15,081.51 |    0.3% |      1.06 | `AddrManGetAddr`
  ```

ACKs for top commit:
  stickies-v:
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Tree-SHA512: 1175cff250d9c52ed042e8807ddc2afd64a806e6f2195b5c648752869ff3beec0be8a8cbd7ab6ba35cd7077d79b88a380da6c6e244f5549f98cdd472808b6d8f

Author: fanquake

src/addrman.cpp

@@ -824,6 +824,7 @@ std::vector<CAddress> AddrManImpl::GetAddr_(size_t max_addresses, size_t max_pct
     // gather a list of random nodes, skipping those of low quality
     const auto now{Now<NodeSeconds>()};
     std::vector<CAddress> addresses;
+    addresses.reserve(nNodes);
     for (unsigned int n = 0; n < vRandom.size(); n++) {
         if (addresses.size() >= nNodes)
             break;