chore: Remove loadKeysFromPfxFiles config

[poulok]

Description:

Platform (CryptoStatic / BasicConfig):
The loadKeysFromPfxFiles boolean config property is removed entirely. Previously, setting it to false allowed the platform to skip disk-based key loading and instead generate keys deterministically at startup for test environments. That fallback path is now gone — the platform always loads keys from disk via EnhancedKeyStoreLoader.

HAPI Test Framework (NetworkUtils, SubProcessNetwork, WorkingDirUtils):
To keep the HAPI tests working under the new requirement that keys must exist on disk, the changes thread the generated keys through to disk before nodes start:

1. generateNetworkConfig() now returns a NetworkWithKeys record (wrapping Network + Map<NodeId, KeysAndCerts>) instead of just Network.
2. SubProcessNetwork stores the nodeKeys map and calls writeNodeSigningKey() after initWorkingDir() — both during initial start() and when adding a node dynamically.
3. WorkingDirUtils.writeSigningKey() is a new method that writes the signing private key as s-private-node{N}.pem into the node's data/keys/ directory, where EnhancedKeyStoreLoader will find it.

Local Node
Local node is not affected because it puts keys on disk prior to starting the CNs.

** Configuration Changes **
Removal of loadKeysFromPfxFiles from settings.txt files that had overrides for local environments.

Net effect: Key loading is no longer optional/configurable — the platform always expects PEM/PFX files on disk. The HAPI test framework compensates by writing the generated keys to disk itself before each node boots.

Related issue(s):
Fixes #24635

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Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.00% (target: -1.00%)	✅ 0.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (98ccacc)	94614	77712	82.14%
Head commit (d51b181)	94606 (-8)	77708 (-4)	82.14% (+0.00%)

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Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#23535)	16	0	0.00%

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Codecov Report

❌ Patch coverage is 0% with 16 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...java/com/swirlds/platform/crypto/CryptoStatic.java	0.00%	16 Missing ⚠️

@@            Coverage Diff            @@
##               main   #23535   +/-   ##
=========================================
  Coverage     78.15%   78.15%           
- Complexity    11679    11680    +1     
=========================================
  Files          2488     2488           
  Lines         94711    94703    -8     
  Branches      10231    10229    -2     
=========================================
- Hits          74020    74017    -3     
+ Misses        16948    16944    -4     
+ Partials       3743     3742    -1     

Files with missing lines	Coverage Δ	Complexity Δ
...n/java/org/hiero/consensus/config/BasicConfig.java	100.00% <ø> (ø)	0.00 <0.00> (ø)
...java/com/swirlds/platform/crypto/CryptoStatic.java	40.00% <0.00%> (+4.38%)	0.00 <0.00> (ø)

... and 7 files with indirect coverage changes

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[poulok]

Note to self: this cannot be merged until LocalNode is updated to generate keys and not depend on the CN generating keys at startup

[poulok]

Note to self: this cannot be merged until LocalNode is updated to generate keys and not depend on the CN generating keys at startup

Upon further investigation, LocalNode does not need to be updated. It is already compatible with this change.