Remove val_exec_ctx feature flag

[plafer]

Closes: #415

Although the diff is big, all that was done was remove the feature flag.

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PR author checklist:

• Added changelog entry, using unclog.
• Added tests.
• Linked to GitHub issue.
• Updated code comments and documentation (e.g., docs/).
• Tagged one reviewer who will be the one responsible for shepherding this PR.

Reviewer checklist:

• Reviewed Files changed in the GitHub PR explorer.
• Manually tested (in case integration/unit/mock tests are absent).

[codecov]

Codecov Report

Base: 55.63% // Head: 55.63% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (388ee98) compared to base (c9c5ee4).
Patch coverage: 5.38% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #414      +/-   ##
==========================================
- Coverage   55.63%   55.63%   -0.01%     
==========================================
  Files         122      122              
  Lines       17076    16996      -80     
==========================================
- Hits         9501     9455      -46     
+ Misses       7575     7541      -34     

Impacted Files	Coverage Δ
crates/ibc/src/applications/transfer/context.rs	35.41% <0.00%> (+0.05%)	⬆️
crates/ibc/src/applications/transfer/relay.rs	0.00% <0.00%> (ø)
.../src/applications/transfer/relay/on_recv_packet.rs	0.00% <0.00%> (ø)
...s/ibc/src/clients/ics07_tendermint/client_state.rs	37.81% <ø> (ø)
crates/ibc/src/core/context.rs	3.88% <ø> (+0.09%)	⬆️
crates/ibc/src/core/ics02_client/client_state.rs	75.00% <ø> (ø)
...ibc/src/core/ics02_client/handler/create_client.rs	35.18% <ø> (ø)
.../ibc/src/core/ics02_client/handler/misbehaviour.rs	53.77% <ø> (ø)
...ibc/src/core/ics02_client/handler/update_client.rs	38.66% <ø> (ø)
...bc/src/core/ics02_client/handler/upgrade_client.rs	64.17% <ø> (ø)
... and 33 more

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[Farhad-Shabani]

All good. thanks