refactor: simplify Eval trait

[meskill]

Summary:
Remove unnecessary restrictions and explicit lifetimes where possible.

Issue Reference(s):
Fixes #... (Replace "..." with the issue number)

Build & Testing:

• [ ] I ran cargo test successfully.
• [ ] I have run ./lint.sh --mode=fix to fix all linting issues raised by ./lint.sh --mode=check.

Checklist:

• [ ] I have added relevant unit & integration tests.
• [ ] I have updated the documentation accordingly.
• [ ] I have performed a self-review of my code.
• [ ] PR follows the naming convention of <type>(<optional scope>): <title>

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 79.87421% with 32 lines in your changes missing coverage. Please review.

Project coverage is 84.15%. Comparing base (2a49da9) to head (df9c1d8).

Files	Patch %	Lines
src/core/ir/mod.rs	57.14%	9 Missing :warning:
src/core/ir/resolver_context_like.rs	50.00%	5 Missing :warning:
tailcall-query-plan/src/execution/executor.rs	0.00%	5 Missing :warning:
tailcall-query-plan/src/resolver.rs	0.00%	4 Missing :warning:
src/core/ir/cache.rs	85.71%	3 Missing :warning:
src/core/ir/io.rs	96.59%	3 Missing :warning:
src/core/path.rs	40.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2207 +/- ## ======================================= Coverage 84.15% 84.15% ======================================= Files 213 213 Lines 20149 20149 ======================================= Hits 16957 16957 Misses 3192 3192 ```

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[github-actions[bot]]

Bencher

Report	Sat, June 15, 2024 at 10:44:08 UTC
Project	tailcall
Branch	2207/merge
Testbed	benchmarking-runner

Click to view all benchmark results

Benchmark	Latency	Latency Results nanoseconds (ns) | (Δ%)	Latency Upper Boundary nanoseconds (ns) | (%)
from_json_bench	✅ (view plot)	7,041,800.00 (-1.15%)	7,256,073.39 (97.05%)
group_by	✅ (view plot)	547.40 (-4.84%)	644.82 (84.89%)
input/args.missing	✅ (view plot)	25.41 (+5.62%)	26.84 (94.68%)
input/args.nested.existing	✅ (view plot)	55.26 (+15.40%)	62.71 (88.11%)
input/args.nested.missing	✅ (view plot)	38.97 (+2.22%)	40.44 (96.37%)
input/args.root	✅ (view plot)	50.23 (+13.76%)	59.43 (84.51%)
input/headers.existing	✅ (view plot)	32.60 (+2.98%)	33.71 (96.70%)
input/headers.missing	✅ (view plot)	31.86 (+3.72%)	33.48 (95.15%)
input/value.missing	✅ (view plot)	23.55 (+0.43%)	24.89 (94.60%)
input/value.nested.existing	✅ (view plot)	38.76 (-6.87%)	45.15 (85.84%)
input/value.nested.missing	✅ (view plot)	34.92 (-4.61%)	38.62 (90.42%)
input/value.root	✅ (view plot)	38.37 (+0.44%)	41.69 (92.05%)
input/vars.existing	✅ (view plot)	7.52 (-4.53%)	8.91 (84.46%)
input/vars.missing	✅ (view plot)	11.21 (+17.70%)	12.82 (87.47%)
test_batched_body	✅ (view plot)	2,656.80 (-99.47%)	2,114,513.77 (0.13%)
test_batched_body #2	✅ (view plot)	1,721,800.00 (+0.92%)	1,832,952.95 (93.94%)
test_data_loader	✅ (view plot)	483,820.00 (+3.04%)	486,938.32 (99.36%)
test_handle_request	✅ (view plot)	155,910.00 (-0.69%)	173,841.09 (89.69%)
test_http_execute_method	✅ (view plot)	18,154.00 (-0.68%)	19,371.51 (93.71%)
with_mustache_expressions	✅ (view plot)	1,168.70 (+0.16%)	1,229.90 (95.02%)
with_mustache_literal	✅ (view plot)	738.25 (+2.26%)	774.41 (95.33%)

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