fix(fork-choice): correct index type in currentEpochTips.del

[rnkrtt]

prune() used physical index for currentEpochTips.del but the table is keyed by logical index. Causes wrong entries deleted after first prune.

[tersec]

The linting CI is failing on:

Run excluded_files="config.yaml|config.nims|beacon_chain.nimble"
The following files do not have an up-to-date copyright year:
- beacon_chain/fork_choice/proto_array.nim

i.e.

nimbus-eth2/beacon_chain/fork_choice/proto_array.nim

Line 2 in ced2b9f

# Copyright (c) 2018-2024 Status Research & Development GmbH

should be updated to read

# Copyright (c) 2018-2025 Status Research & Development GmbH 

[github-actions]

Unit Test Results

       12 files  ±0    2 436 suites  ±0   46m 11s ⏱️ - 1m 46s
12 678 tests ±0  12 113 ✔️ ±0  565 💤 ±0  0 ❌ ±0 
63 716 runs  ±0  62 988 ✔️ ±0  728 💤 ±0  0 ❌ ±0 

Results for commit f8b0cc1. ± Comparison against base commit ced2b9f.

♻️ This comment has been updated with latest results.

[rnkrtt]

@tersec did it, thank you