chore: replace BouncyCastle BigIntegers and Arrays with JDK equivalents

[anthony-swirldslabs]

Description:
CN code uses

• org.bouncycastle.util.Arrays
• org.bouncycastle.util.BigIntegers

We want to replace these with standard JDK APIs to reduce 3rd-party dependencies.

Related issue(s):

Fixes #26792

Notes for reviewer:
All tests should pass.

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[lfdt-bot]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues

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[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...hedera/node/app/hapi/utils/ethereum/EthTxData.java	87.50%	0 Missing and 1 partial ⚠️

@@            Coverage Diff            @@
##               main   #26793   +/-   ##
=========================================
  Coverage     70.47%   70.47%           
- Complexity    11673    11675    +2     
=========================================
  Files          2583     2583           
  Lines        108373   108379    +6     
  Branches      12123    12124    +1     
=========================================
+ Hits          76375    76381    +6     
  Misses        28013    28013           
  Partials       3985     3985           

Files with missing lines	Coverage Δ	Complexity Δ
...hedera/node/app/hapi/utils/ethereum/EthTxData.java	86.79% <87.50%> (-0.08%)	93.00 <2.00> (+2.00)	⬇️

... and 1 file with indirect coverage changes

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1 file(s) changed in commit eaadf51

[testlens-app]

✅ All tests passed ✅

🏷️ Commit: eaadf51
▶️ Tests: 23260 executed
⚪️ Checks: 48/48 completed

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