Merge bitcoin/bitcoin#34937: Fix startup failure with RLIM_INFINITY fd limits

735b25519a support: clamp RLIMIT_MEMLOCK to size_t (Sjors Provoost)
8ab4b9fc85 init: clamp fd limits to int (Sjors Provoost)
4afbabdcef Fix startup failure with RLIM_INFINITY fd limits (Sjors Provoost)

Pull request description:

  When setting the fd limit to unlimited, the node fails to start:

  ```sh
  ulimit -n unlimited
  build/bin/bitcoind
  Error: Not enough file descriptors available. -1 available, 160 required.
  ```

  This was caused by `RaiseFileDescriptorLimit()` (introduced in #2568) casting `limitFD.rlim_cur` to `int`, which for `RLIM_INFINITY` overflows to `-1`. Fix it by returning `std::numeric_limits<int>::max()` instead.

  Some platforms implement `RLIM_INFINITY` as the maximum uint64, others as int64 (-1). So simply changing the return type to `uint64_t` wouldn't work.

  Similarly, though unlikely to actually happen:

  ```sh
  ulimit -n 214748364
  build/bin/bitcoind
  Error: Not enough file descriptors available. -2147483648 available, 160 required.
  ```

  The second commit expands the fix by clamping all values above `std::numeric_limits<int>::max()` instead of letting them overflow.

  This PR also expands `test/functional/feature_init.py` to cover these, using `resource.setrlimit`. The check is skipped on environments with a hard limit below infinity (or that don't have the Python [Resource module](https://docs.python.org/3/library/resource.html)).

  macOS by default has a hard limit of infinity, but on e.g. Ubuntu the default hard limit is 524288.

  The third commit applies a similar fix to `PosixLockedPageAllocator::GetLimit()` for 32-bit systems, but without a test.

ACKs for top commit:
  winterrdog:
    Re-ACK 735b25519a
  achow101:
    ACK 735b25519a
  sedited:
    Re-ACK 735b25519a
  pinheadmz:
    ACK 735b25519a

Tree-SHA512: 0ce0292ecd61456bdec6943b06cbb9ecfc5180ee6dce850f8496ef54af22c1fae6ea473085202f5ba6f72e4dc51a29247620c9a0eae31e96658adc77b293129f

test/functional/test_framework/test_framework.py

@@ -8,6 +8,7 @@ import configparser
 from enum import Enum
 import argparse
 from datetime import datetime, timezone
+from importlib.util import find_spec
 import logging
 import os
 from pathlib import Path
@@ -1082,6 +1083,17 @@ class BitcoinTestFramework(metaclass=BitcoinTestMetaClass):
         if not self.has_previous_releases():
             raise SkipTest("previous releases not available or disabled")
 
+    def has_resource_module(self):
+        """Checks whether the resource module is available."""
+        return find_spec('resource') is not None
+
+    @property
+    def RLIM_INFINITY(self):
+        if not self.has_resource_module():
+            return None
+        import resource
+        return resource.RLIM_INFINITY
+
     def has_previous_releases(self):
         """Checks whether previous releases are present and enabled."""
         if not os.path.isdir(self.options.previous_releases_path):