Reduces memory footprint of collecting unifications.

[esdrubal]

Description

As shown in https://fuellabs.github.io/sway-performance-dashboard/ #6461 introduced a bigger memory footprint.

Lexical scope has a shared OrdMap called symbols_unique_while_collecting_unifications that was never cleared.
With this commit, it is cleared on each code block along with the clear of collected unifications.

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[github-actions]

Benchmark for 0908ac4

Click to view benchmark

Test	Base	PR	%
code_action	5.1±0.09ms	5.1±0.09ms	0.00%
code_lens	290.7±10.98ns	297.2±10.38ns	+2.24%
compile	1924.9±59.74ms	1909.1±52.37ms	-0.82%
completion	4.5±0.07ms	4.5±0.06ms	0.00%
did_change_with_caching	1852.7±17.29ms	1819.5±8.33ms	-1.79%
document_symbol	856.5±25.49µs	849.4±27.13µs	-0.83%
format	73.1±1.09ms	73.1±0.76ms	0.00%
goto_definition	335.9±6.79µs	338.8±9.48µs	+0.86%
highlight	8.9±0.01ms	9.0±0.08ms	+1.12%
hover	346.1±7.62µs	351.8±8.42µs	+1.65%
idents_at_position	118.8±0.68µs	118.7±0.44µs	-0.08%
inlay_hints	640.7±23.76µs	642.3±17.82µs	+0.25%
on_enter	2.1±0.14µs	1963.3±91.91ns	-6.51%
parent_decl_at_position	3.7±0.04ms	3.7±0.01ms	0.00%
prepare_rename	336.3±4.70µs	340.0±7.89µs	+1.10%
rename	9.3±0.01ms	9.2±0.05ms	-1.08%
semantic_tokens	1157.0±14.28µs	1262.7±11.02µs	+9.14%
token_at_position	334.6±2.29µs	342.7±8.14µs	+2.42%
tokens_at_position	3.7±0.02ms	3.7±0.06ms	0.00%
tokens_for_file	400.0±2.66µs	397.6±7.86µs	-0.60%
traverse	34.2±0.57ms	33.6±0.63ms	-1.75%

[github-actions]

Benchmark for 4a622d4

Click to view benchmark

Test	Base	PR	%
code_action	5.1±0.09ms	5.1±0.15ms	0.00%
code_lens	288.6±8.93ns	286.1±10.31ns	-0.87%
compile	2.2±0.07s	1919.8±73.81ms	-12.74%
completion	4.5±0.06ms	4.5±0.09ms	0.00%
did_change_with_caching	2.0±0.07s	1838.8±32.40ms	-8.06%
document_symbol	887.2±37.29µs	911.1±39.50µs	+2.69%
format	74.5±0.90ms	72.8±1.23ms	-2.28%
goto_definition	334.8±5.97µs	339.2±5.25µs	+1.31%
highlight	9.0±0.08ms	9.0±0.22ms	0.00%
hover	347.5±6.22µs	349.8±5.85µs	+0.66%
idents_at_position	116.4±0.41µs	119.1±0.50µs	+2.32%
inlay_hints	640.1±34.34µs	637.4±14.35µs	-0.42%
on_enter	2.1±0.06µs	1956.8±86.34ns	-6.82%
parent_decl_at_position	3.7±0.04ms	3.7±0.06ms	0.00%
prepare_rename	337.0±8.53µs	338.5±6.21µs	+0.45%
rename	9.4±0.19ms	9.3±0.26ms	-1.06%
semantic_tokens	1189.4±15.65µs	1227.6±18.78µs	+3.21%
token_at_position	332.0±2.72µs	337.5±2.32µs	+1.66%
tokens_at_position	3.7±0.03ms	3.7±0.09ms	0.00%
tokens_for_file	400.5±4.07µs	395.9±3.02µs	-1.15%
traverse	36.4±0.79ms	33.5±0.62ms	-7.97%

[github-actions]

Benchmark for 714cb24

Click to view benchmark

Test	Base	PR	%
code_action	5.2±0.01ms	5.0±0.10ms	-3.85%
code_lens	283.3±5.60ns	286.0±8.01ns	+0.95%
compile	1936.4±69.55ms	1824.8±54.29ms	-5.76%
completion	4.5±0.03ms	4.4±0.08ms	-2.22%
did_change_with_caching	1815.8±19.84ms	1768.7±12.07ms	-2.59%
document_symbol	865.5±22.99µs	896.8±36.08µs	+3.62%
format	81.7±1.94ms	82.5±1.21ms	+0.98%
goto_definition	336.4±6.22µs	348.4±5.41µs	+3.57%
highlight	9.1±0.03ms	8.7±0.04ms	-4.40%
hover	346.1±10.39µs	359.5±5.50µs	+3.87%
idents_at_position	117.2±0.30µs	119.0±1.12µs	+1.54%
inlay_hints	643.6±11.86µs	650.8±9.08µs	+1.12%
on_enter	1895.2±41.40ns	1984.3±77.39ns	+4.70%
parent_decl_at_position	3.7±0.04ms	3.6±0.04ms	-2.70%
prepare_rename	332.4±6.58µs	348.0±7.62µs	+4.69%
rename	9.4±0.11ms	9.0±0.49ms	-4.26%
semantic_tokens	1248.9±10.35µs	1195.2±7.90µs	-4.30%
token_at_position	333.0±2.85µs	353.3±1.53µs	+6.10%
tokens_at_position	3.7±0.05ms	3.6±0.03ms	-2.70%
tokens_for_file	401.6±2.32µs	398.0±4.14µs	-0.90%
traverse	32.6±0.90ms	33.2±0.49ms	+1.84%